> I do all of my work on local C:\ paths and copy files to SharePoint or OneDrive only if forced to collaborate with colleagues.

This is an option I considered, but it's harder for non-power users to deal with the file management. It's very likely some users would copy files instead of moving them and it would quickly devolve into trampling each other's changes.

That Dropbox article was great, so thanks. If I had to summarize my issue now, I'd say it feels like the backup solutions have a poorly implemented sync engine. I'm guessing they simply get a stream of changes from SharePoint though and I wonder if it would even be plausible to think they could misapply those changes.