I have no indication that any one spec is more powerful in low level pvp than others. Some classes are just really tanky. You'll' often run into tanks that have queueed as well.
You should use killing spree on a single target if you can.
If there are multiple opponents near each other, run away a bit and then run back to your intended target while spamming KSpree. KSpree will only hit targets in range of Kspree, not the the target, so you can isolate a single target in many cases with a little finesse.
KSpree does not hit breakable cc targets. Gouge/sap/blind will not be hit, so you can cc one person and the ks another even if they are all in range.
Be sure to to apply revealing strike before Kidney Shot for a long 8 second stun. (2 extra seconds). KS is off of DR 6 (or 8) second after the cooldown of Kidney Shot. If you build combo points for a new KS after the cd on KS is up, usually that it long enough for stun dr to wear off.