I guess we disagree about the point of backups then.
We just use different threat models.)
For me, the main threat is disk failure, so I want to get new disk, restore system from backup and continue as if nothing happened.
Surely, if your hardware or OS configuration changes, you should not backup /usr, /etc and other folders.
However, the proposed workflow could be adapted to both scenarios: a single snapborg config backs up snapshots from a single subvolume, so I, actually, use two configs: one for /home excluding /home/.home_unbacked and another one for / excluding /var and some other directories.
This two configs have different backup schedule and different retention policies, so in case of hardware/OS change, I'll just restore only /home backup without restoring /.
Backing up via snapborg allows you to see file structure, because actually it is a file-based backup.
snapperhere allows me to separate snapshot creation from actual backups.