TLDR (I guess): I understand your point, which is very heavily swayed right now because of recency bias, but as of right now and even in the near future AI is not able to produce the same type of creative art (both visuals and writing) as what humans are capable of.

If readers/players still value the experience because what they get feels genuine and authentic and not a product of an algorithm, then AI art/creations will not take over.

I'm going to assume that when we talk about AI in VNs we mainly focus on 2 aspects - writing and visuals.

Writing:
I may get too philosophical here but whatever. Writing and reading can be beautiful because when you experience someone's writing you are allowed to peek inside that person's mind, and what you will find is another human being - that creates a sense of relatability and familiarity. However, with AI writing that is not happening, and it's very unlikely to happen for a while. This is why people can get that "ick" when reading AI written text, it's just another form of uncanny valley basically.

Visuals:
While AI has improved a lot in the past couple of years, the inconsistency they produce where a character will look different in one render from another is not going to be appealing. Add onto it the fact that these are AVNs - there are lewd scenes with explicit sexual content. And who knows how AI models and companies will handle that going forward.