PaulC; the closeness of the aircraft to the baggage reclaim is a benefit to the passenger only in that they don't have so far to walk. For the loaders it doesn't matter where the aircraft is; it will take the same time to offload 150 bags on a stand at LHR as it will at SOU. The big difference is that at SOU the passenger will be in the baggage reclaim waiting, whereas at LHR they'll still be on the route march to the baggage reclaim!
It also takes the same time to offload the bags onto the delivery belt, as the speed of the belt drives how quickly bags can be offloaded. This is set at an optimum speed which allows pax to be able to lift bags off the belt with relatively little effort rather than being dragged around cartoon style as they try to avoid their arms being pulled off!!