Given that the martial arts teacher, like the magic teacher, wasn’t a master of such a degree either, Erwin’s group in their current condition would be too much for him to handle as his own strength wasn’t that different from theirs.
Even if they couldn’t use magic, in case they were martial arts experts, they preferred the direction of earning an income as adventurers.
Therefore, expect for becoming a temporary advisor, it would be strange for them to become full-time instructors at a prep school. It was a truth that those were quite rare.