@Ahodegozaimasuru
in reality now or back when it's a game?
if it's this reality, then in short normal NPC can't afford it, since it requires early carry or good eq to 1v1 your first summon (has been explained early in the story, along with other people above elucidating further the problem why)
if it's back when this is still a game, the meta is warrior class
nine sages were a bunch of magicians who gathers in one guild to tweaks or minmaxing build so that it can match the meta
also, luminaria, meirin, and valentine can dish out more damage than mira