> I've never been able to properly work on a Word document together with a colleague. Not even once
Many millions of others seem to do it all the time without issue. I've done it practically every day for many years now and haven't run into sync issues for a long time.
It's not made to sync if two people are trying to open the file off a NAS, it's made for people editing files stored in OneDrive/SharePoint.
But as both examples show, you need to have your document editing and document storage closely working together for multi-user live editing to work. That's something that so far practically only integrated editors/storage platforms offer.
Google Docs, on the other hand, works great when you're working together on a document. Too bad they don't have a native client.