Playing on a bad team will wear any goalie out over a long season, which Gibson has done for 4-5 years now. Anaheim also sells off at the deadline every year which is when the numbers get worse. When you watch him play he is constantly barraged with lots of shots and chances and no person athlete or not is going to be able to have the same drive and compete when the score hits 4-0 and then ends 7-2 for example. Especially when it happens so often. Having watched the Wings during their most recent really bad run, the goalies got burnt out from all the bad defence/games in front of them and as the season wore on, their numbers plummeted and overall play as well.
I don't care what the backups do, as they play less and are generally starting against the worse teams. Give any of his backups Gibson's workload of the past 4-5 years and I highly doubt their numbers look very good at all.
I think if you put Gibson on an actual good team, that team will be more than happy with his performance.