Wow, didn't know this thread would blow up so much. I feel like I should clarify my position.
I think sorc dps does great in ranked 8v8s. Having people to hide behind, 1-2 tanks and 2ish healer to protect them, the sorc does great. Also, most people don't utilize their offheal potential as much as they should.
However, in 4v4 arenas, that is not possible. There is no back line. There are only 4 of you, and if two warriors jump to you, you cannot heal. You cannot really kite (due to the lack of root-resistance from force speed and there being two of them with roots). You cannot really cast unless you have polarity shift (10 seconds out of 2 min). This is where I feel the weakness of sorcs is. Casual makes it work for them from what I've seen, but it is definitely a sub-optimal comp.
My two cents.