Nick Bee over at GotFrag interviewed members of Evil Geniuses (previously called Frag Dominant), and revealed a few points about the Arena that many casual players don't necessary see. While Nick doesn't actually say to which member he talked, the interview doesn't seem about the individual as much as the team.
When asked about perceptions of Frag Dominant, the Evil Genius responded that before the MLG San Diego tournament (which they won), the only really available basis for opinions was from the Tournament realm and other tournaments. But his real point is that since Frag Dominant could run multiple class compositions using the same players, they had a very good chance of winning -- their adaptability was higher than other teams'.
He reinforces that idea of composition flexibility at the end of the interview. The Genius says whether you like it or not, you need to be aware of WoW's metagame if you're going to compete seriously in the Arena. (This means each person on a competitive team should have experience with multiple classes, and how the dynamics between those classes change.)
I think this outlines an idea that many folks miss about the Arena. Arena competition isn't just about your character competing, but also the players behind the characters. I could be the best Hunter to ever tame a pet -- but I probably don't bring much to a team if I can't tell the difference between a Silence and an Interrupt. Your skill isn't just fast-twitch reflex or single-class knowledge: it's overall knowledge about the whole enchilada. In the midst of nerf-calling, we should keep in mind that player skill doesn't just mean "skill at my class."