I've built a document editor that has AI properly integrated - provides feedback in "Track Changes" mode and actually gives good writing advice. If you've been looking for something like this - https://owleditor.com

It looks nice, but for my use it's very specifically not reviews I want in AI integration with an editor, but to be able to prompt it to write or rewrite large sections, or repeated references to specific things, with minimal additional input. I specifically don't want to go through an approve edit by edit - I'll read through a diff and approve all at once or just tell it how to fix its edits.

Claude at least is more than good enough to do this for dry technical writing (I've not tried it for anything more creative), and so I usually end up using Claude Code to do this with markdown files.