Fiction requires charting a path through the infinitely large space of what is possible. I think AI can be very helpful assistant when plotting, figuring out how you lead characters naturally, as the storyteller, to where you want to get them through manipulation of circumstance.

One is limited as a writer because of the hard problem of bringing to attention possibilities you haven't considered yet (ie writer's block). AI can be very helpful as a search tool for the "possibility space" even if its judgment and voice are mediocre.