When I say "messages" (in art) I'm not talking about, for example, the simple Aesop-level fable messages--the obvious metaphors. I'm talking about emotional experiences--statements about what it means to be human.

How can a non-human entity know what it's like to be human?

I absolutely do think that AI can and will replace simple books written by simple authors whose only goal is to crank out an easily digestible story that will entertain a reader for a few hours. Yes, those kinds of writers will almost certainly be replaced by AI.

But that's a very different kind of book from, say, The Grapes of Wrath or The Good Earth or Beloved. I don't think a non-human mind, no matter how technically brilliant it may be, could ever convey the emotional weight of important literature, because it will never understand what it means to be human and to experience a human life.

ETA: The reverse side of that same coin is also true: a human author will never be able to write a novel about what it's like to be an AI that will feel true and resonant to an AI. A human can't understand what it's like to be an AI, either.