Why didn’t Airbus put something in place as well when introducing the A321?
Because it does not need it, Boeing is removing them from the 777-300ER. Bumpers don't stop tail strikes, or prevent damage.
A RAD ALT on the tail link into the pitch computer and a filter than resists further pilot input.
No aircraft works that way.
why not have proximity sensors in the tail linked to pitch channel; both take off and landing?
Inertia, with the small ground clearance and pitch rates, you add complexity to a tail strike that is going to happen before it makes contact.