Probably that is good enough for the synchronization issue. The central server runs a prune process once a month, which might generate another headache …
Additionally I was a bit concerned about integrity of the backup under the circumstances, that the server messes things up, e.g. local driver error, but I can probably handle this with the pre-check (as described).
I might end up with a second restic rest server on the desktop machine and a script to trigger the backup of the backups from the server to it, which should address the synchronization and potential data error issues, but obviously not the performance impact.
From my perspective the safe duplication of backups would probably be worth a more general discussion.