@Noiro
Even if he did, he wouldn't be able to do anything. Or rather, he wouldn't be ALLOWED to do anything.
First, even if he did decide to do something, everyone else is stronger than him, even the asshole. He'd be beat down.
Second, knowing that the mission is important to them (not to the readers, of course), he wouldn't allow himself to do anything because as insufferable as the asshole mage is, he's still a vital member.
Of course, if MC tried, then he could figure out a way to take out the mage, but like I said, knowing how important the mission of defeating the demon king is, he would stop himself.
Also, if he did manage to do something, it probably wouldn't be the members who would bring MC down, it would most likely be the countries backing the heroes.