Use Shirtaloon's He Who Fights With Monsters as your case study.
He spent 20 months writing his first volume offline (roughly 350k words) then started posting on RoyalRoad with a large backlog for patreon. After he'd written and posted roughly one million words of content for free he published to Amazon through Atheon.
Obviously, he put a ton of work in and nearly two years of his life before even putting the story up for free, but he's been very successful now.
It's better than 95% of the Kindle Unlimited LitRPG and Urban Fantasy stuff. It isn't as well written as popular Fantasy authors, like Sanderson, Martin, Abercrombie, McClellan, etc. But I would consider it on the level of Dungeon Crawler Carl.
It technically isn't a game, but the mechanics work the same and it definitely falls under LitRPG. It has problems here and there, but far better than most LitRPG I've read. The characters feel distinct, there aren't typos or missed editing, 'I' and 'me' is usually used correctly, unlike most Kindle Unlimited books. The mechanics are interesting (kind of similar to Will Wight's Cradle, I wouldn't be surprised if it took inspiration) and it's an interesting premise, but the mechanics all still work like a game, HUD, etc.
I would recommend strongly "He who fights with monsters". I both it because my subscription was expiring, and it was... long. It litRPG, so it's basically a fantasy book, but the characters have stats and skills like in games. It doesn't affect the plot that much... maybe makes it a little growth-oriented (leveling) up. It's actually a really good book, disguised as trivial fun.
It's not strictly a cultivation novel but has some elements to it, but I have been enjoying 'He Who Fights with Monsters'. Book 1 is on KU and is over 1000 pages:
https://smile.amazon.com/gp/product/B08WCT9W26
I am not into harem novels that much.
'Silver Fox and the Western Hero' is primarily a cultivation novel mixed with Wuxia. It hints at a harem to come but has only hinted at it in the romantic interactions.
Affliction Specialist. Great series. _He Who Fights Monsters_
https://www.amazon.com/He-Who-Fights-Monsters-Adventure-ebook/dp/B08WCT9W26
Welcome to the genre! Here a couple of recs:
1) Soulstone series by J.A. Cipriano
2) He Who Fights with Monsters by Shirtaloon
3) Alpha Physics by Alex Kozlowski
Two self recs: Level Up and God of the Climb
Currently reading Dungeon Crawler Carl myself (on Book 2!) and it has been a hilariously excellent read. Great way to start the genre.
My top recommendation that I think fits your request is He Who Fights With Monsters by Shirtaloon. Not only is it well-written with a great system and engaging MC, the surrounding cast is fantastic, and it includes some light romance. This story is a banger, so treat yourself to it once you wrap DCC.
He Who Fights with Monsters: A LitRPG Adventure https://www.amazon.com/dp/B08WCT9W26/ref=cm_sw_r_apan_glt_ZDWFPPRSB40K4MMVPMS7?_encoding=UTF8&psc=1
Once you are done with that and if you still want more, you can try out my novel, Dive: Endless Skies, which is currently a contestant in SPFBO 7. It's a more traditional fantasy setting about a young woman who falls in with a team of guild mercenaries on a Dungeon quest. You can expect great characters, good action, a little romance (more just awkward flirting and budding romance), and light litrpg elements.
Dive: Endless Skies (The Dive Sequence Book 1) https://www.amazon.com/dp/B08XQVLJBL/ref=cm_sw_r_apan_glt_1TBZZF75RAMTV6CWJZY7
He Who Fights with Monsters by Shirtaloon has been great. Combat is fun and the dialog is increadable. I would avoid the audio book as it falls into the trap of having a stat sheet that is read out but the book for me is a must read. I would desibe this a a Isekia/Gamerlit with some great character building.
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Swing Shift by William D. Arand (Randi Darren is the same author) is another great book filled with modern fantasy fun. I would describe it as a mix of fantasy/mystery/action. All of this authors books share the same universe which is a plus.
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I would also recommend Demon Accords series but I would say it has some inexplicable character moments that really brought the series down as a whole. The Power Creep is also off the charts.
He Who Fights Monsters. Magic everywhere
Done of what I have found enjoyable in progression fantasy
He who fights with monsters https://www.amazon.com.au/He-Who-Fights-Monsters-Adventure-ebook/dp/B08WCT9W26
Cradle https://www.amazon.com.au/Unsouled-Cradle-Book-Will-Wight-ebook/dp/B01H1CYBS6
The ten realms https://www.amazon.com.au/Two-Week-Curse-Realms-Book-ebook/dp/B07F7QQGZ9
Elemental gatherers https://www.amazon.com.au/Azyl-Academy-Elemental-Gatherers-Book-ebook/dp/B07TFSC77N
Coiling Dragon, I found went on just a bit to long so I did get bored towards the end, but otherwise a great read https://www.amazon.com.au/Coiling-Dragon-Book-Saga-ebook/dp/B07FRGNGMJ
I read The beginning after the end, and found the first 4 it so books great, but started getting bored after that. https://www.amazon.com.au/Early-Years-Beginning-After-Book-ebook/dp/B01B1DNB3C
Non standard progression fantasy or sci-fi settings
Modern setting progression fantasy Street cultivation https://www.amazon.com.au/Street-Cultivation-Sarah-Lin-ebook/dp/B07W9J75R3
Progression fantasy sci-fi Emerilia https://www.amazon.com.au/Trapped-Mind-Project-Emerilia-Book-ebook/dp/B01MZD5RQX
Progression sci-fi https://www.amazon.com.au/Starships-Mage-Glynn-Stewart-ebook/dp/B00QW6ZG14
Standard fantasy with progression elements.... So many, but a few I have enjoyed include The demon accords Wheel of Time Spellmonger Dresden files Histories of Drakmoor
Looking at my past Kindle Unlimited selections, a few jump out at me for how much I liked them:
<u>He Who Fights With Monsters</u>
<u>Lings</u> (Not actually LitRPG, but if you like Starcraft, you'll probably like this)
<u>Bio Dungeon</u> (If you ever thought to yourself "I wish I could combine dungeon core novels with my favorite anime, Cells At Work!", well, here you go.)
<u>Queen In The Mud</u> (People have been asking for female MCs, non-human MCs, and not-another-spellsword MCs. Naomi, the Salamanderkin water-mage and eponymous Queen In The Mud, is all these things and more!)
<u>Mage Errant</u> (Another that's not necessarily LitRPG, but has one of THE most interesting magic systems I have ever read about, even if it's not very crunchy)
Goodreads is weird, cant figure out which instance is the right one, but this is He Who Fights with Monsters. I read it last week. Damn good book actually and its serialized adventures which was a nice change of pace.
If you're looking for protags using poison or general debuffs, you can't go wrong with He Who Fights With Monsters by Shirtaloon. The main character is an affliction specialist and focuses on debuffing and one-on-one attrition fights.
A heads up about reading it though- the series started on Royal Road for free, but I think within the last week (?) the first book's chapters have been removed in preparation for an official Kindle release on March 9th. https://www.amazon.com/He-Who-Fights-Monsters-Adventure-ebook/dp/B08WCT9W26/ref=sr_1_2?crid=YMX4WUPG0EC5&dchild=1&keywords=he+who+fights+with+monsters+a+litrpg+adventure&qid=1613869371&sprefix=he+who+fights+with+monster%2Caps%2C-1&sr=8-2