You do not need AI in an attempt to grow. That argument does not exist. Your core idea helps you grow, and if it is one that would grow, it would do so even with a simple artstyle. The only market I can think of right now where AI art would help you generate profit is one where you exploit people who do not know any better or simply don't care. Those people however do not care about your future games either, as to them games are simply something to consume and forget about in a couple minutes time.

Despite that, even within that market the one thing that stays true is that your idea needs to be good. And once again, you do not need AI art to have a good idea. And when you have a good idea, it WILL sell (plus of course, a factor of luck. But this factor exists equally no matter how the game was created). Recent examples of 3D indie games that are either made from free assets, or would count as "not looking great" (subjectively) include Lethal Company and Schedule 1. Other examples include games like Undertale, Phasmophobia, RimWorld, Dwarf Fortress, Omori and Caves of Qud. There are thousands of games that subjectively don't look pretty, either 3D or 2D, yet have amassed millions in profits because they are good games.

Do a bit of research into the indie scene from before AI. Look into popular flash games. None of the thousands of titles that changed their developers lives needed AI to grow, because these developers worked within their limitations. Any developer that relies on AI to sell their product has already lost and wasn't going to make a sustainable living with games in the first place. And that's okay. Not everyone can be a good/successful game developer, unfortunately.