One thing people are missing is the dungeon Haruka is in isn't a normal dungeon. It's mentioned a few times, but I think the manga glossed over it. The dungeon he's in is the most powerful and oldest dungeon in the region. Basically, he's in the bonus post-game dungeon. Instead of a Dungeon Boss, or a Dungeon King, floor 100 had a Dungeon Emperor.
The Otaku are power gaming the shit out of the world, and the Jocks turned out to be battle maniacs that only went into sports because Japan has no need for Paladins and Samurai. And even they haven't gone down past level 45 or so.