DK and Pala are OP at the moment, but there's a wider problem that has been in place since TBC and got a lot worse with WOTLK - burst damage. The burst damage from most classes is totally out of control. I agree about the idiocy of a self-healing, high dps class in plate, but the reality is that plate doesn't mitigate much damage in PvP these days, plate wearers take a couple more hits to kill is all. What gives Pala and DK the edge is their OP abilities rather than the plate. Pala v pala duels don't last as long as you'd think, the burst damage takes care of that.
I've done some PvP in the Bgs with my hunter (now 80 with full PVE epix) and I can kill most classes in a few short seconds. Of course the flipside is that if anyone gets on my case I also die in even less time (I don't even bother trying to kite, it's futile). Resillience also seems to mean nothing anymore. Dunno how the arenas are, I've never done them, but over the years I've played a lot of BGs and the quality of the PvP game experience has gone over the edge of a cliff. You could argue that high burst damage is what people want and Blizz are catering to that, but ask most people and they say they hate it so I think the reality is Blizz screwed up by constantly buffing gear and they can't find a way to rebalance things.