You don't need the expert raw app to shoot in raw. Just switch over to pro mode. It's basically the same thing as expert raw. And yes it does appear Epix will edit RAW images.
That being said, Epix doesn't appear to be much different than the stock Samsung photo editor. It has more but for basic corrections it's the same.
Photo editor is a far more capable app. The user interface isn't very good though. Actually the user interface keeps me from using it.
Touch retouch is the app to use if you want to remove objects and stuff like that. Very nice user interface. It works magic like Photoshop.
But the Samsung stock editor will erase objects too if you click on the 3 dots. I'm not sure if that's a labs feature or not. To enable extra features in the gallery and editor, go into the gallery, click on the three lines at the bottom right, choose settings, choose "about gallery", and click repeatedly in the middle of the screen in the blank area. Keep clicking and a pop-up will say "gallery labs enabled". Then you'll have extra options in the gallery settings. A pop-up will appear when you've almost clicked enough times. You have to keep clicking to actually activate labs.