No, that isn't a 3v3 arena team. Though it could work decently, I guess. It'd be better if we got a Rogue or a Hunter to replace the.. um.. well, the Moonkin.
I've been working on leveling two of my least favorite classes to PvP against - a Frost Mage, and a Shadow Priest. So here are my current impressions:
Frost Mages are gods of control. No one gets close to them, thanks to a permanent uptime of chills and the frequent freezes. What makes them quite overpowered, however, is not just the control - it's that controlling their target goes hand in hand with bursting them down, thanks to talents like Shatter and Fingers of Frost.
Survivability is also amazing. Blink, Ice Barrier, Ice Block, and Mana Shield guarantee that it will be a while before I die, so long as I have mana. My Mage is a Gnome, so I have extra mana, and a racial to make me even harder to catch.
Shadow Priests are a bit less about control, and more about melting faces. I kill mobs my level simply by applying DoTs and wanding, and there are still a few seconds to go on both SW:P and Devouring Plague when the mob dies. 1v1 PvP is ridiculously easy - keep PW:S up, apply DoTs, cast Psychic Scream, cast Mind Blast, spam Mind Flay. You dead yet? Yeah you are.
Mana was an issue at the lower levels - I'd have to drink every 1-2 pulls, despite Spirit Tap. Attacking two mobs at the same time meant almost certain OOM-induced death. Now, however, my mana is much better thanks to the Replenishment effect. Health is never an issue - Improved Vampiric Embrace is way overpowered.
The gameplay is quite different, that's for sure. My Moonkin's PvE control is fine, mostly thanks to Typhoon and Entangling Roots. However, my PvP control with the Mage or Priest is much, much higher. It feels so good to Counterspell / Silence some poor fellow trying to heal.
That being said, it all does feel a bit awkward - mostly because I am so used to playing as a Moonkin. When my health is plummeting, my reflex is to shapeshift the hell out of there while spamming HoTs on myself. When I am getting close to dying on either of my alts, I feel a rising sense of panic - usually, I've no idea what the hell to do.
Not being able to heal on my Mage feels dangerous, as I haven't yet been accustomed to their way of surviving: controlling their opponent to death, mainly.
I can heal on the Priest, yet the style is different and also feels bizarre. If Psychic Scream and my bubble are gone and on cooldown, I feel at a loss. There is some strange force that makes me hate dropping out of Shadowform to Renew or Flash Heal - definitely not a problem I have on my Druid. But we will see how it turns out at end game, when I have more survivability talents and Dispersion.
All in all, I still stay true to what I've said before. Mages and Priests are overpowered. They might not be downright facerolling classes, but they are very, very complete classes. They have all of the tools they need to melt faces, and more.