One tactic I've adopted for general 4x shammy pvp for Mage AOE spammers is to hit my spread out macro:

Shammy 1 Nothing
Shammy 2 Back diagonal left
Shammy 3 Back directly
Shammy 4 Back diagonal right

So that the mage cant hit all of the chars at once, and I'm pretty much guaranteed that my nuke from at least 2 of the shammies will hit him even if he's jumping around like a blue arsed fly. Before I just used to stay on follow and it tended to hurt a lot more. Now they go down quick and I loose a max of 25% health. once they are dead, I rehit follow to reground and ensure I have range on further targets.

I'll sometimes do he same for annoying/skilled rogues to make sure they go down, but in general in arenas I ignore them.

Non arena note on rogues though, is as I have 3 LWers, I put drums of panic into my melee counter totem rotation. Doesn't work in arenas ofc, but they are cheap to make, and give you a couple of seconds to heal up/blast even if they trinket/wotf out of it. People definately dont expect shammies to fear