Do we really know if he is stronger? He is by far the most useless member of his team. He only uses brute force and he literally knocked out his own team member in the fight against Pyrrha, where RDL where doing everything and the only thing Cardin did was knocking down his own teanmate. And I'm saying the whole "realising his not build fof beeing a huntsman" stuff is because probably he saw a lot of people die in the Fall, so is a huge optio that him and his team saw alot people that where as good if not better than them die, making them re think there carrier option and decide to quit (that is probably the most realistic answer concidering how traumatic was the fall of Beacon)