I think AA as well as UA/DL started the "priority bags" as an elite perk well before the proliferation of baggage fees. But one of the unintended consequences of baggage fees is the (what I assume) skyrocketing number of gate checked bags.
They ramp guys are trying to get the plane out on time, they aren't worried about putting gate checked bags behind the priority ones. Same with the ramp guys at the destination, they're just trying to pull everything that needs to go as quickly as possible.
This would also explain why Asian Carriers are better as most of their flying is Long Haul where everyone gets a free checked bag. So their ramp people get used to it and better at it.