Developing good games is hard. The minute you add sexual content, you're not only pushing your game into a niche and losing most of your market, but you're also pulling resources away from polishing that gameplay.
The premise is faulty from the start.
The problem is not that gameplay isn't polished, the problem is the market is not interested in that kind of gameplay you provide.
You need to be a Great Game in a Genre they are Interested. So not only do you need to be in a Demanding Genre to make, but you also need to be Great and Crush your Competition to have enough Value.
With Sexual Content you are changing the whole Motivational factors and Value system.
RPG Maker games without Porn are
Not Viable in the market.
RPG Maker games with Porn are
Viable with enough Sexual Content.
Furthermore there is no problem of Competition since the Value of Sexual Content is Evergreen.
The reason "Simple Games" are Not Viable is not that they aren't enjoyable, most people can enjoy simple flash games/mobile games and the like.
The reason they are Not Viable is because they don't have enough Value for either Money or simply Time investment, players have better options.
But with Sexusal Content you always have Value and the "Content" is immediately "Consumed", you can only fap so many times to the same scene, we always want "novel" sex scenes, with new girls.
TL'DR: Make Porn Games with Simple Gameplay you dumbassess.