How much of an impact does story and world building have on H-games, especially rpg games?
Well, it have none impact, would answer the members that only play to fap. But in the same time, near to as many members would answer that it's something fundamental, because what interest them is what hide behind the lewd, both linking the lewd scenes together and justifying them.
Which way you'll goes finally only depend on you, but it seem clear by looking at the support games get, that story less games can only succeed if the lack of story is compensated by a strong, and coherent, game mechanism. What tend to point as player interested only by the lewd content to be less pron to support a game they like to play.
So, I guess that the question is: Do you want a game with many players, or do you want a game with players that will support you ?
Knowing, of course, that anyway the chance to have enough support to live from your game are near to null. But, depending on the choices you made for the game (game engine, CG type and source, etc.), even a small support can be enough to cover your costs, and then having a lot of players become an interesting motivator since it address directly your ego.
I want to start making an rpg adult game and i have a hard time deciding if the story and worldbuilding should be complex or not.
Well, then I'm tempted to ask you how many storyless RPG you've seen in your life. I'm pretty sure that the answer is near to zero, because what is the interest to play a role, when the role to play limits to "exist and live" ; with "and also fuck", due to the nature of your game.
The instant there's no role to play, the RPG mechanism are just a burden. It's the reason why many games are seen as useless grinding. The lack of effective role, and generally also story, make what could have be seen as "raise your cleaning stats" looks like "there's nothing in my game, so to occupy you, repeat that stupid useless task again and again".
I dont want to impact the adult side with the lore side, if that is possible.
Whatever choice you make, it will have a negative impact on your game.
There's globally as many players who want to fap, and players who want a story spiced with lewd. The first ones will despise a game with too much text, while the seconds will not care about a game that have lewd content that seem to pop out of nowhere.
What fall back on the only possible answer to all "how should I make my game" kind of question: Do it the way you want it to be, period.
The chance that you end in the less than 10% of adult game creators that earn more than US$ 5,000/month are near to null, this even after years of existence. So, your motivation should be the pleasure you take working on your game, what can only be achieved if you do it like
you want it to be.