At least with the "user vs admin" distinction, I could argue that it is useful becase my backups could be stored into a separate account with restricted access, so ransomware running in at the "user level" account, would not be able to touch them.
While if my "admin" account gets compromised then all bets are off as the backups could be wiped out (even if they are offline, they could be wiped out the next time I connect the storage device).
However I find a much harder time finding user justification for having a separate "root" vs "manufacturer root", unless you happen to be a manufacturer with questionable motives. If root is compromised, the attack surface becomes absolutely huge, and it doesn't seem to be very useful as a user the fact that I can rely that at least the kernel and bootloader will not be compromised if everything else is dubious.
Sure, now I can trust that the builtin "restore to factory" functionality on the device works (and even that may not be true). But unless I use it frequently (and who does?), the malware with root access would still be able to destroy all of my files anyway, compromise my backups, etc.