I found that MS Word was excellent for a long book (240 pages). It’s use of styles, footnotes, indexing and table of contents were brilliant for long documents.
The only reason I moved away from it was that it couldn’t produce PDF of the correct specification for printers (which it turns out is a killer problem!).
It wasn’t great for fancy layouts or fancy backgrounds for headers or footers or that kind of thing of course.
The PDF export problem is the biggest killer for it though IMO. If you can’t use it to produce something to send to a printer…
I’ve been using an old copy of InDesign 6 for the longest time, but it was so flaky and at some point will just top working, so I’m delighted that Affinity Publisher is looking so positive.