The imbalance is the expertise advantage. People wouldn't be doing as much damage without the expertise stat. I see Juggs and Guardians critting 10k, Snipers and Gunslingers doing 6-8k, Operatives and Scoundrels doing 6-10k, Sages and Sorc's stacking dots, and cc's, Shadows and Assassins doing 5-8k, Powertechs and Vanguards doing 4-8k, Mercenaries and Commandos doing 4-8k.
Everything is fairly balanced, it's just those who have the battlemaster/champion gear compared to those who don't, is a huge advantage, which makes them seem overpowered.
I personally as a sage, have no issue with any class, except Juggernaughts and Powertechs. Yeah operatives can be annoying, but once I live through their initial stun, I shield, dot them, heal up. They try to vanish, dot ticks them out, and I destroy them.