> For example, "Making the slightest change became a chore. [1.] Update the 'master' DOCX. [2.] Update the InDesign file ..." --the appropriate way to use an external document as master in InDesign is to use the Place command, which autoupdates text changes as they are made in Word.

It does not auto-update. Even if it did, you wouldn't necessarily want it to auto-update, because it's very hard to tell if changing one sentence in your manuscript has borked the layout of dozens of pages. Once you have rules set up around widow and orphan control, it's very easy for even tiny text changes to have large downstream layout effects.

Also, frankly, InDesign is kind of flaky and will sometimes change layout or make other visual changes in response to apparently nothing at all. I ran into a bug where it would just silently drop underlines on some elements and jiggling them a bit would bring them back.

For my two books, I ended up writing a script that would generate a visual diff of the entire book from the PDF export of the InDesign files so that I could tell for certain if InDesign had gotten itself confused. InDesign can produce beautiful output, but like a lot of Adobe software, it's temperamental and opaque.