Are you a fighter or a backlininer

I recently noticed somthing while playing, the one who are suposed to be at the back (saper medic priest) are usually the one that fight the horde during holdout event (at the middle of San Sebastián when you gotta dig at vardeous fortress ect) so I got a question when you play a class more based on support do you stay at the back or do you said duck off and just don’t give a dang about the rest and just play as if you were the doom slayer?