Tina's is my level. I've nearly completed that on my Psycho and they were scaling with me. Unless you mean 'The enemies are getting leveled up by the Witch Doctors to level 59' I can't see why they'd be higher on Hammerlocks.
Ah maybe that is what was happening with the witch doctors. I was fighting lots of mobs while trying to protect Hammerlock while he fixed a boat or something. I got my ass handed to me by the ones he had levelled up.