The remake of Spriest in MoP was really really terrible. Cataclysm spriest was almost absolutely perfect. All that had to be done was to make a more powerful/fun dps CD, and increase the single target no ramp up time burst by a tiny bit. I realised that spriests were kind of shit to play already at the MoP pre-patch (like who the heck designs that shit?). After less than a month at lvl 90 I decided to reroll to warlock. And that was after maining shadow priest ever since I rerolled from holy/disc to shadow in late Tbc. At least the demo warlock was extremely fun to play in back when I raided heroic modes in 5.0 and 5.1.
I couldn't really give a damn about numbers that much (as long as it is bearable). If I can't make it out of the 5man heroic progress stage without falling asleep because the spec I am playing is terrible then I couldn't really care less about 25man heroic BiS numbers.
Unless they completely revamp shadow priests again, I guess I am going to play my warlock once again when I activate my account when the new expansion arrives. It's quite sad though. I have a lot of rare stuff on my priest that I would love to use but can't since the only dps spec they have is depressing to play. It amazes me how Blizzard managed to make spriests the ranged ret paladins in MoP (shit ton of procs) but without any actual cds to compensate. And all of it was because a couple of people complained about the damage being slightly affected my rng the first 20 seconds of a fight (like that ever mattered over the course of a 10 min heroic raid boss).