I mean at this point just ditch the Unifi? You have a much more capable gateway in play now that needs to have equal to greater throughput than the one you are bridging for.
No, the half-bridge is less capable for various functions, but happens to have hardware PPPoE offload which makes it faster for this specific function but not for others
I always suspected this was possible but having it demonstrated is excellent. I would assume this would be of most benefit on an OpenWRT box which _does_ support hardware offload!