SL absolutely destroys once you get full r10+ gear, you've got SO much HP and because you split the dmg with your pet they take forever to kill. You don't do massive damage with the spec, but you take forever to kill. I played with a r14 SL lock who was our FC from time to time because he simply would not die. He had something like 6+k hp buffed with fort, it was insane.
Banish the pet. SL is gone.
But yes, locks are really strong in PvP, regardless of the spec.