I do ubers fairly easily with abyss lock. Are you spamming miasma bolt on them to make the clouds disable their HP regen?
But yes, single target damage is pretty garbage for abyss until you ramp up the stacking clouds. PTR reportedly nerfed the clouds damage by a lot so I expect it to be much worse on PTR that it is on live.. haven't tested and cba to. I still love abyss because it's one of the coolest looking skills in the game XD
oh actually havent been using that i just use the abyss skill and nothing else