I feel this is a false equivalence.

Atomic updates are not the same thing as backups.

Backups: my file is gone, overwritten, corrupted, I accidentally deleted contents I want... but my computer is working, so I will retrieve a copy from my backup.

Atomic updates: aargh, my computer was half way through installing 150MB of updates across 42 packages, but one file was bad and the update failed, so I rebooted and now it won't boot! No problem, reboot to the boot menu, choose the previous snapshot, a known-good config, and you can boot up and get back to work, until the update is available again.

Didn't say they were equivalent, I've said Borg is enough for me, specially when pacman does a very good job updating the system atomically. In the rarest cases where a pacman update breaks the system, which is usually when the user doesn't have informant installed and forces a failed installation, I'd just chroot from an arch live install disk and fix the OS.