I like how the arena boss is happy to be beaten - since it's proof of his strength that the only way to beat him is to cheese out a billion (while it's still also a reminder that he can be beaten, making fights a bit more interesting for him again)
at least rex got something from this duel, now he can change job into sword saint just like nirva
the job that can only be unlocked if you defeated him in the arena
there's quite a lot of lore detail left out from the WN tho, like nirva is not the only npc with OP stats, there's 3 more people just like him
and there's some explanation why nirva is so OP stats-wise because he never supposed to join your party, thats why he got boss stats