Everyone has their own favourite tool for writing, and there's not necessarily a need to change it. If you prefer to write in Google Docs and then copy and paste into WordPress, and any negative aspect of doing so (formatting etc.) is less of a problem than simply writing in the Gutenberg editor, then all power to you.

I agree that neither the old editor nor the more recent version are perfectly-tailored for long-form writing. Writing-specific apps, which have a very narrow focus and feature sets, are much more likely to provide a better environment for the one task they're designed for.

However, one of WordPress's strengths has always been that if you want it to work in a specific way for you, you can install a plugin to achieve that. The Gutenberg editor makes that way more possible than with the “classic editor”. I've used the editor in WordPress since its first version to blog, both short- and long-form, and the “classic editor” was always a pain to work with. There was no possibility to move paragraphs around inside the text, and God forbid that you wanted to add a couple of images in an appealing column layout.

If I were going to run a site where pure writing were the focus, then the Iceberg plugin looks like the leading contender to me.