So, since the Arena enemies get gradually more health and damage output at the arena, would you say that the increased difficulty levels are some sort of mini OP lvls?
Sure, our own gear doesn’t scale, but that actually adds to the challenge. A bit like doing Borderlands 2 OP lvls with your lvl 72 gear maybe.
Yes/no/maybe?
Half a yes. OP levels applied to the whole game and the gear. But arena difficulty is still “extra challange for better gear”. I’d be willing to bet that the devs wanted to add something like the OP levels for the masochists of BL2 
I kid, I kid, it’s alright in co-op, which this stuff was designed for
The Arena only becomes sort of like OP levels when you debuff yourself. Not before. Also notice the sort of.
Arena level 7 = BL 2 UVHM though.
seems to be more like just playing with extra people. it sticks around when you leave, just like going to raid bosses arenas could make the players set to 4