

Overwritten is fine when that is intentional. But the best backups do include media that is completely offline and so if there is an issue you can restore to fresh/new uncompromised systems.
ZFS snapshots are great for this - so far they have not been attacked and when they work they give you what the file was before. (you still should have an offline copy of everything stored in a different campus)

fair. Though that seems like it will shutdown the fediverse. Either because you can only connect if you personally know someone to get you an account (that is chain of trust - because we have proven to validate our users we will federate), or because their are no instances.