SCRIVENER has many very useful functions that MSW doesn't, but in the end I have send a .docx to my editor, and it falls flat right there. You can Export from Scriv to .docx but then you're right where you'd be if you wrote in MSW.

I'm doing an experiment: Reformatting a 150k word .docx as follows. Set tabs to auto 0.25, manually making all Chapter headings - Heading 1. I think I can Import into Scriv using Separater #, which will make each Heading 1 into a separate chapter, and give me all the Scriv functionality.

My only reservation is in preserving that formatting during my editor's Track Changes.

Scriv is hard to beat in outlining, general organization and especially research, and Exports to eBook file formats.

Hearing good things about Vellum, a finishing application for .docx. Microsoft doesn't seem interested in Independent Authors, so newer, more hungry developers are running away with these programs.