Alright, now consider this:
1: Weapon and defense skill would only influence the amount of critical hits and crushing blows that the enemy is likely to perform. They have nothing to do with the actual power of the hit otherwise.
2: A twinked character, like the sort they brought to the dungeon, would have stats equal to someone 10-15 levels over them who is in leveling gear.
So if they’re using characters with stats equal to that of level 40-45 characters, why shouldn’t they take damage similar to that those characters are taking?