I tried pasting some paragraphs from my work in progress novel into ChatGPT, and asked it to "improve the writing". The output was exactly the kind of crap you'd expect from someone well read but with no writing experience. E.g. way too many adjectives, and reading as if it had been written by looking up every other word in a thesaurus. I tried having it add some paragraphs, and similar thing: A whole lot of beginner-level writing of the "first he did X, and then he did Y. A bit later he did Z" type of writing. And that's testing just the very superficial language issues and ignoring plot entirely

It's impressive it can even do that, and it'll improve, but anyone looking to these tools to generate good fiction at this point will be disappointed.