@Owyn He is really OP, just that he hasnt been fully optimizing what he has yet.
He has a 1-hit kill sword, ability to rapidly level up, teleportation, ability to learn new skills just by touching items, ability to slow down time and immensely broken commerce ability (purchase price reduction and sell price increase). If you compare to the world, going from dungeon level 1 to beating a level 7th floor boss in less than a year is borderline lunatic.
The dude that died before spent years on 1 floor only to get killed at the end