How much do you use the word highlighting? I'm on Linux and thought about a tool like that and had no idea it existed. How good is it actually?

My main problem with such an editor would be that I wouldn't bother writing for example this nostr reply in a different tool. I'd want it integrated in the browser with it having access to the full context. Then, the possibilities would be endless. 

 LanguageTool, you mean? I constantly use it, though I've now lost the native MacOS app. The Firefox extension works very smoothly.