In my experience, warlocks are one of the classes I have no problems killing off. It's almost as if shadow priests are the counter class to locks.
But I will agree that our dot protection is really bad at the moment.
Personally I think that all of our dots should have an effect if removed.
VT - same as it is now.
Pain - Gives us a free shadow orb to spend.
DP - Heals us for a bit.