Hi
As an old OwnCloud User I’d add the fact that the decision to use UUIDs was already made in OwnCloud, before the fork to NextCloud. Earlier, Usernames were used and visible in OwnCloud, then only these UUIDs. The reason was overlapping usernames, however that happened…
-> most likely culprit was the then fasionable conversion from ISO to UTF8 Formats - along with the ensuing mess. Some Distris, like SME-Server, “converted” the saved Samba Passwords to something not workable anymore… ;-(
Not really a good decison in my opinion, Usernames should be unique anyway.
The present UUID “feels” like a MS-License Key or the like to most IT users… 
But that’s how it happened…
Andy