The O365 integration with OneDrive is so seamless relative to other options, employees won’t even complain after an initial learning curve. In fact, many will start subscribing to O365 on iOS etc. and start having access to the same content synced across Windows, MacOS, iOS, Xbox, etc.
At this point, with employees adapted and the “M365” data visibility and DLP tools switched on, the enterprise can switch off Dropbox or other file depots so even personal accounts won’t work.
It takes a year or so to play out, but that’s how you lose 20,000 customers at a time.