From rolling a new sniper alt all I see around my level are mercs, sorcs and ops.
I honestly don't think sorcs or mercs are really OP, maybe need some small changes but nothing big. Ops there are TONS of people who have re-rolled as one now. The funny thing is they are mostly bad and I kill them on my sniper.
The thing about this game is there is a huge disparity in how hard classes are to play properly. Sorcs, ops and mercs are all really easy to get big impressive numbers without using many keybinds or much of a thought process.
Most of the other classes require a lot more skill and require the usage of many more abilities to be played to their maximum effectiveness. My assassin, for instance, has about 12 abilities I use on a regular basis that all have CDs of less than 30s. On top of that I have another 5-7 abilities (mostly CC/defensive) with 45s+ CDs that are also used regularly.
When a merc/sorc/op can use 5-10 abilities and do just as well or better I can understand why people re-roll.