Level 40 Assassin here. I have been pvping since level 12, valor level 25 and not once did I ever feel I was under-powered in there. Im 100% madness spec and most people just run when they get in pvp with me which is not possible thanks to all my stuns(electrocute, whirlwind, creeping terror, force slow, force speed) Even if they do get away from my 10m range I can still nuke with a 3k death field.
I think the biggest thing people don't understand in pve is that we have this AMAZING skill called Dark Charge. Once khem val loses aggro stop being a noob and switch to dark charge for a free extra 25% mitigation and more heals. Its not there just for looks people. Also in pvp as well, switch to dark charge when there is a melee guy on you, or your running the huttball, or trying to run away to a health pack. Or just force shroud/force vanish
If I hear this class is under-powered I feel bad for the marauder/dps jugg forums...