A CPU serial number or other ID is more unique than a MAC address, as those can be spoofed, and are not guaranteed to be unique, either. I heard one case of someone tearing their hair out over a mystery network issue, eventually discovering two NICs with the same MAC. And also the case of someone buying a whole pallet of NICs, which turned out to all have the same MAC address.

But I don't think that math checks out. A player driven away might return, but a banned player can't.