That not true at all a pve geared hunter, rogue, or mage could beat someone in full pvp gear easily. Warriors and death knights can't touch a good hunter. Mages can just straight up kite someone all day long have two ice blocks, and massive amount of cc to stop damage. I never understood people who whined about pve gear in bgs if your good enough it was just a damage boost.
Btw this is in a cata and wotlk perspective haven't played a dps at 90 yet leveling a rogue.