People are to quick to point fingers at a highly represented class when they lose a match.
That is a very good indication. It is most definitely a good place to start investigation. There is something wrong when Spriests are preferred to an ele shaman/boomkin or a warlock in 3s.
While I won't question the strength of Void Shift (although if the other team is good enough at reacting, it can backfire), I feel like the answer to your question is due to the relative strength of boomkin and elemental.
I have less experience with boomkin, but ele at least has always suffered in small scale arenas thanks to their vulnerability to being focused. It has gotten better with the addition of SR to their toolkit, however they are still EXTREMELY vulnerable to interrupts and CC. Additionally, some of their toolkit is actually better utilized with other specs (It is harder to effectively use Capacitor Totem as Elemental than it is as Enhancement, for example).
As for boomkin, I'll let someone more "in the know" about the spec give input. From what little I have seen in the past, they also suffer from vulnerability to CC with their only upside being the one-trick pony of Solar Beam + Vortex (which is more of an RBG thing, in terms of effectiveness). They can be more elusive, sure, but yeah.
I think the trend of Spriests being so popular in 3s is pretty simple to explain. Despite all of the nerfs, instant CC and burst damage are still higher than what we have seen in the past. Spriests fill a very necessary need in that they provide some decent CC alongside strong burst offhealing. Keep in mind that our strongest utility abilities require either setup (VE) or a long cooldown (Void Shift, and to an extent VE). I'm not sure what the answer is for Mass Dispel, but I do feel like to remove it in a world with so much insta-CC would be about as effective as attempting to remove silences in a world with instant cast heals.
IOW, something for another expansion when they decide to make such major changes.
Don't bother to check my XP. While I have around 150-200k HK's on my account, I have not PvP'd much seriously since Vanilla. I do attempt to stay abreast of info as it becomes available, but I rarely have the time to put in to do anything worthwhile in that environment.
We have taken several nerfs already in regards to our PvP toolkit, and as a standalone I do feel that we are in a good spot right now. The problem is that without something resembling a spriest, arenas would be a very unsettling place right now. I'm afraid this is the "new RMP," as it were, in terms of "this is what happens to work the best for the current world we play in."