I don't think many of you are looking at the "Big Picture."
I'm not here to hate on Blizzard or anything but look at it this way. The game is dumbed down for the casual players, correct? For the players that only play once or twice a week for a few hours. (Not that there is anything wrong with this.) Why? So Blizzard can make more money off with a wider market range. So this creates a problem with the different gear players will get at end game. LFR creates one tier, normal instances the second and heroic versions the third. This means the scaling will naturally be way too high when it comes to later gear (for progression to exist you must need better gear in order to down a boss before the enrage timer.) So since there is a HUGE difference in the item level of gear with PvE there must be the same with PvP.
Three tiers: Honor gear, conquest gear and Elite conquest (I know there isnt elite for 5.2 but hear me out). They need this so there is some sort of barrier between the hardcore players and the casual players. (For their market; nobody who plays this game frequently would play if you could only get regular honor gear. If you are 2.2k and put a lot of time into this game you don't want the same as someone who puts in 2 hours a week).
Due to scaling in MoP everyone's damage is high, their healing is high and their health pools are high. Why? You need a large difference between the last expansion otherwise players wouldn't bother doing anything to attain the new gear (and this leaves a chance that you will get bored, unsubscribe and Blizzard would lose money). If you could do MoP raids/pvp with Cataclysm gear then whats the point to attaining new gear? (besides looks obviously).
Now take into account that Blizzard wants to balance this game around RBGS. This makes sense because Blizzard simply wants players to have to work together in a larger group that is (overall) easier to balance. This also gives a reason for letting their developers get a little lazy with pvp. Simply scale class damage for pve and in RBGS it won't matter as much. So now you're stuck with players who have ridiculous damage, have a high amount of life and insane healing in a game where there is very little actual balancing to any sort of skillful play. Making it more casual (After all, who doesn't like to see large numbers?) and overall "easier" for the players and on the developers since they won't have to worry too much about players complaining.
Basically, Blizzard is just being very lazy and very greedy. Catering to a larger crowd which will bring them more money. There you have it, my theory on why PvP is no where near as good as it could be.
Now, lets talk about ways to improve the PvP.
1. Take away certain abilities in Arena only. Whether that is spec specific or overall for the class, who knows.
2. Make it so PvP gear is very similar to PvE gear and give players buffs/debuffs for when they enter arenas.
Thank you for reading the post and please be kind!
EDIT: Sorry if my thoughts feel scattered, it's 5am here and they certainly are.