This app was mentioned in 9 comments, with an average of 1.67 upvotes
the issue could very well be just with Touchwiz's messaging app. have you tried other messaging apps? this is a great alternative. I suggest you give that a try before trying to downgrade.
Oh, okay, I figured it out! I've been using the stock Messaging app that came with my phone instead of Google Messenger, which I'm guessing is the new stock messaging app.
EDIT: Hm ... it doesn't minimize the YouTube app, but it still requires that I pause the video to reply to texts. Either way, multi-window support would resolve stuff like this entirely.
even as someone who also hates Touchwiz, I would simply replacing and customizing everything you can on the Touchwiz rom.
install Nova Launcher, install Swiftkey or the Google keyboard, install this AOSP based messaging app, ES File Explorer, the CyanogenMod calculator.
root, install Xposed framework and Wanam, install Titanium Backup Pro and freeze or remove all of Samsung and Verizon's garbage. there are a lot of other really nice tools in the Xposed Framework, and there are other root apps that I might suggest, but your main goal is to get this phone to not feel like Touchwiz as much as you possibly can.
my suggestion is to make your Note Edge be as tolerable as possible until you can get a custom rom for it. from my perspective, it doesn't seem worth giving up a new phone just for software, because the software can always be changed. that's one of the greatest things about Android.
I used "Messaging" for a year, still had lagging and sucked at MMS, so now I'm trying the stock app after the Lollipop update.
I'm surprised nobody has answered your question yet. as a person who can't have his devices without root anymore, I can easily find you root apps to do anything. Touchwiz on my S4 especially, my root apps are the only thing that make it tolerable for me. Samsung's software is a giant mess.
first a few basic apps that don't use root. I highly recommend Swiftkey, Nova Launcher and this AOSP messaging app. in the case of Nova Launcher, you can customize everything about your home screens with it. the AOSP messaging app is just a cleaner UI and something I have thought to be a better messaging app as a whole. Swiftkey is regarded as the best keyboard on Android, as far as look and feel, and on top of that, it learns how you type, so the auto-correction becomes less annoying and more helpful. there's also ES File Explorer, which can be given root access to act as a root file manager if you go through its settings, but isn't necessary, and I would recommend it regardless, since it's a great file manager.
now onto root stuff. Titanium Backup Pro to back up your apps and data, as well as freeze apps, which disables Samsung and AT&T's garbage without deleting it. I freeze KNOX on my Touchwiz roms, and pretty much everything else that annoys me or gets in my way that's pre-installed. next I would suggest AdAway, which blocks ads system-wide. the only downside is that redirects through Google shopping search results no longer work, but I would argue it's worth the trade to never be bothered by an ad again. something else I use is called Light Manager, and it makes it so I can customize how the LED notifies me about certain apps. color, frequency, and adding your own apps to choose their color. I have it set so that Play Store notifications blink white, Trigger blinks yellow (so when I tap a tag with my screen off, it notifies me with the light.)
next is a big one, the Xposed Framework. this app gives you what are known as modules, which give you an amazing amount of options with your phone. one of the biggest ones for Touchwiz users is called Wanam, and it allows you to modify a lot of how your phone looks, feels and operates. GravityBox works similarly, but it's designed for AOSP. I use it on my S4 as well, but not everything in it works properly, and I mostly use it to change the functions of my nav buttons, for example, double tapping back switches to the previous app, and holding down menu takes a screenshot. in your case, on the S5, you could make your recents key back into a menu key and make long-pressing home bring up your recents again. another module I have is called App Settings, and it lets you change screen rotation and toggle screen timeout per app. for example, I always want my messaging app, among other things, to only be portrait, so I have it set to always be portrait. there are Xposed modules for pretty much everything. I have one to make it so my NFC antenna works with the screen off so I can tap tags without unlocking my phone. I have one that moves some of my directories, like pictures and downloads, onto my external SD card. I have one called Statusbar Gestures that lets me slide across the bar to open certain apps. I have one called Burnt Toast which puts an icon next to the popup notifications so you know which app says what. my biggest advice is to look through Xposed and pretty much download anything you think is interesting.
I hope this all helps you enjoy using your phone a bit more and helps you get the most out of the device.
with all due respect, you're not using Nova Launcher because...? it can import all your icons, it gives you much more to customize, you can change the grid size to fit more icons on the screen that's clearly large enough to have your home screens be 5x6 instead of 4x4.
It's not safe for me to flash anything custom on the AT&T Galaxy S4, but with stuff like Nova Launcher, ES File Explorer, an AOSP messaging app, CM calculator, the Google Keyboard and Swiftkey, my phone is much more usable, Touchwiz is much more tolerable, and it's generally a better experience.
alongside all the non-root stuff I've replaced, with root, I use things like Wanam and GravityBox to tweak just about everything, from UI elements and colors to what my nav buttons do, to disconnecting my ringtone and notification tone volumes, and much more. I also use AdAway to block intrusive advertisements, the App Settings Xposed Module to stop certain apps from rotating, Light Manager to customize LED colors for certain apps (which has a lot of functionality without root as well), and Titanium Backup to freeze apps like KNOX and other AT&T and Touchwiz stuff that gets in my way, and of course to keep my apps and data saved to my SD card. there's a few other basic root utilities that I use occasionally, but nothing that really affects usability of the phone like all the stuff I just listed. assuming that you're not rooted and you're on a firmware supported by Towelroot, it's literally as easy as downloading and running a file off the internet to root your phone if you're curious.
if you give a try to some of the things I do, it will feel like a new phone. it's incomparable. I needed most of that just to make the phone tolerable for me. running this phone completely stock would be unbearable for me. I love Samsung's hardware, but their software is one of the worst modern Android skins to exist. it has improved significantly over the years, but there's so much better you could be doing, and I think you should try experimenting. my suggestion is to at least start with Nova Launcher.
If this is what you're talking about, you can find this one on the store :) https://play.google.com/store/apps/details?id=com.softcoil.mms
I'm sorry to say that right now, there's not much that can safely be done. I also have an AT&T Galaxy S4, and I'm still on the MF3 firmware, never updated it since I got it, froze the updater, and I still can't do anything safely from this much earlier update. much more was restricted since if I'm not mistaken. if you want CM on the AT&T or Verizon variants, you need to have modded it when the phone was first released, which not many did.
with that said, I've made Touchwiz tolerable by rooting it and modifying everything that I could. it's still not as capable as CM would be, but there isn't much else you can do. if you haven't already rooted it, I can help find you a guide if need be.
without root, you can install things like Nova Launcher, Swiftkey, this AOSP based messaging app, VLC for Android, ES File Explorer (which can also be enabled as a root file manager), and this remote app which is infinitely better than WatchOn if you care about your IR blaster.
with root, even on Touchwiz, you get much more freedom to customize, almost on the same level that CyanogenMod would give. Titanium Backup Pro lets you freeze all of Samsung and AT&T's garbage, which disables it without deleting it. Titanium is also the best Backup utility on Android. AdAway is system-wide ad blocking, and the only downside I see is that if you look through Google Shopping results, the redirects sometimes don't work. I also use an app called Light Manager, which you can use without root, but root adds a lot of functionality to it, such as choosing your own apps to have different lights. without root, there are only a select few preset apps that work.
also with root, you can access the Xposed Framework and many of the modules within it. primarily, you're going to want Wanam, which lets you change quite a bit of how Touchwiz looks, feels, and operates. I also have GravityBox installed, which does the same thing with AOSP based roms. being designed for pure Android, not everything in it works properly, and I mostly used it to modify how my nav buttons work (ex. I have it set so long pressing my menu key takes a screenshot, and so that double tapping back switches to the previous app). there's a module called App Settings which lets me customize things like screen rotation and screen timeout per app. there's a module called Burnt Toast which puts the icon next to the pop-up notification, which I have found to be useful when trying to identify what app is telling me what. there's also the Download2SD module which lets me change the directories for my pictures, downloads, etc. to my external SD instead of manually needing to copy everything after. I also use a module called Statusbar Gestures which gives me quick shortcuts by sliding across my statusbar. aside from those, I would highly recommend that you just scroll through Xposed and look through all the modules to see what you could use. there's plenty of stuff that you might find useful that I have no need for.
I hope all of that helps you out a bit. if you want to know anything else, let me know. as somebody else suffering with my AT&T S4, I made it so I could still love this phone without a custom rom, and I'd like to help you do the same.
I'm surprised nobody has answered your question yet. as a person who can't have his devices without root anymore, I can easily find you root apps to do anything. Touchwiz on my S4 especially, my root apps are the only thing that make it tolerable for me. Samsung's software is a giant mess.
first a few basic apps that don't use root. I highly recommend Swiftkey, Nova Launcher and this AOSP messaging app. in the case of Nova Launcher, you can customize everything about your home screens with it. the AOSP messaging app is just a cleaner UI and something I have thought to be a better messaging app as a whole. Swiftkey is regarded as the best keyboard on Android, as far as look and feel, and on top of that, it learns how you type, so the auto-correction becomes less annoying and more helpful. there's also ES File Explorer, which can be given root access to act as a root file manager if you go through its settings, but isn't necessary, and I would recommend it regardless, since it's a great file manager.
now onto root stuff. Titanium Backup Pro to back up your apps and data, as well as freeze apps, which disables Samsung and AT&T's garbage without deleting it. I freeze KNOX on my Touchwiz roms, and pretty much everything else that annoys me or gets in my way that's pre-installed. next I would suggest AdAway, which blocks ads system-wide. the only downside is that redirects through Google shopping search results no longer work, but I would argue it's worth the trade to never be bothered by an ad again. something else I use is called Light Manager, and it makes it so I can customize how the LED notifies me about certain apps. color, frequency, and adding your own apps to choose their color. I have it set so that Play Store notifications blink white, Trigger blinks yellow (so when I tap a tag with my screen off, it notifies me with the light.)
next is a big one, the Xposed Framework. this app gives you what are known as modules, which give you an amazing amount of options with your phone. one of the biggest ones for Touchwiz users is called Wanam, and it allows you to modify a lot of how your phone looks, feels and operates. GravityBox works similarly, but it's designed for AOSP. I use it on my S4 as well, but not everything in it works properly, and I mostly use it to change the functions of my nav buttons, for example, double tapping back switches to the previous app, and holding down menu takes a screenshot. in your case, on the S5, you could make your recents key back into a menu key and make long-pressing home bring up your recents again. another module I have is called App Settings, and it lets you change screen rotation and toggle screen timeout per app. for example, I always want my messaging app, among other things, to only be portrait, so I have it set to always be portrait. there are Xposed modules for pretty much everything. I have one to make it so my NFC antenna works with the screen off so I can tap tags without unlocking my phone. I have one that moves some of my directories, like pictures and downloads, onto my external SD card. I have one called Statusbar Gestures that lets me slide across the bar to open certain apps. I have one called Burnt Toast which puts an icon next to the popup notifications so you know which app says what. my biggest advice is to look through Xposed and pretty much download anything you think is interesting.
I hope this all helps you enjoy using your phone a bit more and helps you get the most out of the device.