Emacs has an amazingly nice editor, especially for writing in plain language. It even supports right-to-left languages and things like Sanskrit. There are frequent posts in /r/emacs about using it for writing. Many novelists use Emacs for writing, some of them are well-known names - Cory Doctorow, Neal Stephenson, Vernor Vinge, Charles Stross, et al.
There are a number of nice packages that help you with writing - spellchecking, thesaurus, dictionaries, translation, definition and etymology lookup, LLM integration, export capabilities, distraction-free modes, various text manipulation tools and more.
The joke that Emacs is an operating system that simply needs a decent editor has not aged well. It's not even funny in the slightest; it's laughable in the face of the joke teller, telling more about them than Emacs and its editing capabilities.
