zfs send is also a general purpose file sync tool, it just has the limitation that server side and client side must use ZFS.

The advantage of RSync is that it is independent of the file system - which is at the same time a huge disadvantage of RSync, as it prevents RSync from performing optimizations which zfs send can do.

> zfs send is also a general purpose file sync tool, it just has the limitation that server side and client side must use ZFS.

That's… not general-purpose at all. zfs send is a specific-purpose tool, the specific purpose being to serialise and output a ZFS snapshot.