I suppose you’ve looked at cwRsync. rsync.net has commentary here (and their own product…).
Yes. It does need to look over the whole file at both ends, although I think rsync is also read-heavy.
Very sophisticated software sometimes uses Changed Block Tracking (CBT) instead of scanning.
I talked about that here, and mentioned Veeam and UrBackup, but I don’t know how they restore…
On the backup side, you probably want at least a crash-consistent one, and you might want more.
If your database is VSS-aware, several backup programs (including Duplicati) can work with VSS.
Because you mentioned rsync, perhaps consistency is OK already (maybe you shut DB down?).
Comparison of file synchronization software Commercial section shows some block-level syncs.
Wikipedia doesn’t have that listed for free software, but Syncthing has some sort of delta support.
The manual says very little, but you can see people in the forum discussing its benefits and limits.
If folder and other issues can be solved, DropBox and some OneDrive do differential (delta) sync.
That ended mid-comment, but maybe you were going to note Task Scheduler can run CLI restore.