@Vincent Berg
In fact, for promising stories, I've often copied the text and transmitted it to Word so it's easier to correct the many, many typos and mistakes.
On the contrary, it's FAR, FAR easier to do that in BBEdit with Grammarly than in Word. Far less bloat, no silliness with Word formatting, and the ability to change every instance of a string across 15,000,000 words in 2s or less. Ditto for searching for any string (including regular expressions) across all 15,000,000 words in 2s or less. Text replacements can also include regular expressions.
In addition, by having the files in a private GitHub repo, I can trivially roll back to any version of any individual chapter (ditto with my backups, though they don't respect versions the way git does, just what happens to be on disk at the time).
Markdown feeds directly into Scrivener, where I can set all the formatting rules, by output type (ePub, PDF, Word) and that formatting doesn't interfere with my text in any way, shape or form. Oh, and none of it is proprietary.