The problem isn't the granularity of the backup but since the worm silently nukes pages, it's virtually impossible to reconcile the state before the attack and the current state, so you have to just forfeit any changes made since then and ask the contributors to do the leg work of reapplying the correct changes
Why would nuked pages matter? Snapshots capture everything and are not part of wikimedia software.
The nuke might be legitimate?
That's not a lot of state lost. Destructive operations are easier to replay than constructive ones.
Is Wikimedia overreacting then?
No: from what I can tell, they're being conservative, which is appropriate here. Once you've pushed the "stop bad things happening" button, there's no need to rush.