1. I can't comment on Warrior, since I haven't played that class in any expansion past WotLK. Paladins, while vastly different in terms of throughput abilities, their utility spells remain largely the same.
2. Opinions differ, but I find WotLK more "balanced". Not because of health and damage numbers, but because of how simplified many things became with the changes made to the game in Cataclysm.
3. Rets, no. They usually get steamrolled by the better pvp players, especially casters. Those who complain about Rets being "OP" are usually by the less capable players. Holy paladins do pretty well, though. DKs aren't necessarily part of the strongest comps for the patch, but it is a very strong class on its own, and is viable in various arena comps.
4. Yes.