Not that I agree with using local accounts instead of domain accounts but fair enough.
It's much better than the old way of home folders in a file share.
arguably subjective
Yes, of course. IMO OneDrive is much easier for the end user instead of having to remember to store files in a share or using folder redirection which is prone to fail sometimes. Because using OneDrive they only have to store files where they normally store them and they get automatically synced and backed up to OneDrive. Something being easy is a huge benefit because it will ensure documents and everything else is backed up properly and it reduces support load.
Please tell me you have some kind of backup of those computers where you don't use shared storage or apparently anything "proper".
You don't use Windows home too, right?
Btw, GPOs only work using a domain. You are probably using local policies and those are sometimes not as likely to work.