It still answers your question if you comprehend things. The people using the dungeon are only on floor 1 of it. The loot’s increased with the difficulty. The hero is a whiny shit that doesn’t coordinate his party well. Like every other “MC booted from the party” tropes, the MC seems to have been the one actually leading the team and probably tanking or drawing aggro. It’s not that hard to figure out.
It doesn't answer the question at all.
First off, page 12, the adventurers state that if they level up a bit more then can reach floor 2 faster. Meaning, they already use floor 2. Hero's party only went to floor 2 (it's not written on the manga but the novel states it).
Secondly: MC was really weak before. And he doesn't seem like he is a strategy genius or anything. Contrary to a lot of "exiled" mangas, MC wasn't the unkown strong ace of the hero's party. Probably he wasn't a dead weight but he wasn't the driving force. (No seriously, the hero's party is shown to have better strategy than MC. MC just brute force everything).
Thirdly: in chapter 20,
the hero's party kills a bunch of demons that ordinary adventurers couldn't do anything. The martial artist even succeeded in drawing the aggro of the boss for a moment, while A and S class adventurers got killed instantly. The hero's party is strong compared to the majority of adventurers. Maybe just the hero isn't that strong, but the rest is quite strong