Another thing on this issue; it helps prove my point. During Firelands progression, we recruited most of a 2400+ RBG team, using the logic you mentioned, if they can pvp at that level, raid bosses should be no issue. Most of them were cut after 2 weeks for being way worse than our pretty pedestrian raid team. They would have smoked any of us in a BG or arena setting, but they were awful at raiding.
My mistake, I had assumed that top arena teams had burst macros, cc chains, interrupt rotations, etc., and would be aware of the how each comp would utilize those things against them. I didn’t realize that they were all just winging it out there. Thanks for clearing that up for me.