@Doramas - the way I see it, the priest was powerful, but too immature to babysit this bunch of teenagers. He could not even gain their trust to learn about their problems.
Sure, it might have worked, if the team had somebody else to do the babysitting. You know, the king could have sent his best maid, or the castle's cook, or the Queen's bodyguard, something.
But he didn't, and the cardinal had no excuse for sending MC as the party's priest, because he knew that. I'm sure he could have sent a sagely old man, or even went himself. And don't tell me the cardinal didn't know the Hero would need babysitting. It's pretty much a given when you summon a random noncombatant from another world.
In fact, with the way the cardinal goes about being sneaky, I'm sure he knew the Hero was a woman, and could have told it to a female priest before sending her on the mission.
Yes, babysitting is traditionally a priest's job. And the cardinal's chosen person is just as much of a political choice as the nobles who sent their beloved daughters.
But ultimately, the country just skimped on sending a suitably large expedition.