The benefit of using something fancier than rsync is that you get a point-in-time recovery capability.
For example, if you switch the enclosures weekly, rsync gives you two recovery options: restore to yesterday’s state (from the enclosure not in the safe) and restore to a state from 2-7 days ago (from the one in the safe, depending on when it went into the safe).
Daily incremental backups with a fancy tool like dar let you restore to any previous state. Instead of two options, you have hundreds of options, one for each day. This is useful when you mess up something in the archive (eg: accidentally delete or overwrite it) and don’t notice right away: It appeared, was ok for awhile, then it was bad/gone and that bad/gone state was backed up. It’s nice to be able to jump back in time to the brief it-was-ok state & pluck the content back out.
If you have other protections against accidental overwrite (like you only back up git repos that already capture the full history, and you git fsck them regularly) — then the fancier tools don’t provide much benefit.
I just assumed that you’d want this capability because many folks do and it’s fairly easy to get with modern tools, but if rsync is working for you, no need to change.