"Was this out of his subconscious need to further depersonalize and dehumanize those whom he meant to characterize as evil and deserving of punishment, or was it simply the expedient of an artist who didn't want to have to draw a bunch of different characters?"
I wouldn't go with the latter.
I mean, he could just have started off with one main guy to punish, or even used this exact same set up and make every but make each step of this overly elaborate gauntlet into a punishment into itself: one gets the claw, another gets the cobras, another gets fused to the rock...