Major spoilers
Kondoh, while not being the priest, did indeed become more useful than Yua during the purification since even the priest wasn't strong enough to completely purify the mana. Yua despite being the current chosen priest is just a very naive high school girl. And Kondoh being a 29-30 year old corporate slave relies more on brain than he does feelings.
The higher up's are basically using the priest title to excuse child labor and the fact that they don't want to think about the long-term problems and just use the fastest way, and if it happens again they'll leave it to the next generation so they can summon yet another priest deal with it. But I mean come on, she's just 16, being a priest ain't a part time thing. I don't think they even gave her the option to go home yet
(P.s. I can't remember if they do summon multiple priests or not since I read these in my spare time and that's at 1-4 AM so I might be wrong on that)
Mc is the Saint and the Saint is the “extra”
Isn’t that kinda believable though? Saint is being stupid, a Saint is supposed to save people and Mc originally tried saving the Saint when she was being sucked in in the first place, he just failed to do so, and everyone assumed the Saint was the girl. Though I know that’s not it bc Mc doesn’t have magic.