Exactly, Karryn’s Prison is a game done by REM that focuses only on coding and have 5 years of exp doing only that, while Sachinama did the artwork for the game and the result of this is amazing.
But i would dare you to look at Sachinama old games were he did coding + artwork and try argue they are as good as Karryn's Prision or Melty's Quest.
Basicaly i am not arguing that is impossible to learn how to use RPGM on 5 years, what i am saying is lone coding is not as easy as you think it is, most well done projects either are done big specialized teams or if you do it alone it will simply take a lot of time.
But i am absolutly open to reconsider that if you show any example of a game you know that was done solely by 1 person and was great and was done quickly.
Caliross, just off the top of my head, i saw a similar question before and someone listed around a dozen single devs with high quality games and regular updates. I would list more games, but i'm not following which games are made by single devs and which are made by teams, but there is quite a few of them.
The Way was also made by a single dev, but he got discouraged with how unpopular it was for no reason and eventually dropped it. Defenestration was made by a single dev too, but he eventually started milking patrons too, and then his country got attacked (Ukraine).
Oh, and don't be like "i am not arguing that is impossible to learn how to use RPGM on 5 years", it's impossible to NOT learn it in a year of using it, so stop with the semantics.