Damnation becomes way too easy when you reach 30 and get lvl 30 legendary weapons. Gear doesn’t need to be good even, just lvl 30 with random modifiers really. Damnation feels like Legend in V2. Gear grind is fun, but once you get BIS gear the game is just easymode. Just run at enemies and they die. When you have played every map, mission, condition, done every challenge penance, obtained the best possible gear, what should be then left is self improvement, improving ur skills, challenging yourself.
Damnation is fine, just make a 6th difficulty, it will improve replayability.
And don’t just add more gunners it’ll just slow the game down and not add any difficulty. Bigger hordes, bigger groups of armored folks etc
EDIT: and I am not even good at the game, during V2 I barely managed to clear Cataclysm, and that was with the best possible gear, had to clench my buttcheeks the whole run.