Is he serious? Finding someone with the potential on facing those "universe" monsters would be impossible on such a undeveloped world. He'd be better off increasing his strength, go to another world, and increase the strength again, now that he finally got the 4th crest. It'll take him like a few thousand years if he gotta train a party.
Also, if he want's to find someone so bad, then he can't help anyone. They have to prove that they can get stronger by themselves, without a third party basically babysitting them constantly.
Also, how stupid is the principal? He already basically said that our MC is the strongest person on the school. Why'd he need to be with a party in the dungeon?