That guy isn't a failure of a hero. He's the bloody demon king with those beyond OP skills. Was this actually the whole scenario created by the goddess? Summon a group of people, separate one unpopular person from among them, make that person even more unpopular, and fill them with hatred towards the others and the world? The bulk of the summoned people will be the heroes, the singled-out one will be the one opposing the heroes, that is, the demon king. The goddess then sent the MC, with the ridiculous skills, to a dungeon full of walking experience points to give the new demon king a healthy boost. He's alone, after all, against all the heroes. It's like the script for a reality tv show for the local deities.
I can't view this in any other light.