Well, (and this is not to just dismiss your complaint) one of the biggest problems people had with the original Borderlands was how even the highest level enemies were totally outclassed by a level 50 character. One of the DLCs rebalanced all of the enemies in the game.
I'm not sure how it works in B2, there are definitely some zones where enemies stay permanently low level but others seem to scale. I'm sure there's some pattern.
I can understand the complaints, but I think this goes in the complete opposite direction. I'm not really seeing a good balance here. The game really seems thoughtless when it comes to single player. Sometimes I'd go through areas and have 50+ enemies spawn, and then I'd go back through the same area again with someone only to have 15 enemies spawn. It really seems off.
Anyway, just beat it. The final boss was