They were overpowered before, but the change to pvp power has made them nearly immortal. Blizzard plainly has design problems with healers in pvp, and the proof is the "battle fatigue debuff." Basically they don't know how to design healers correctly in pvp so they threw a band aid fix blanket nerf on all healing in pvp.
However, even with the band aid fix and healing debuffs from certain classes, it still takes 3 to 4 geared players to bring down a single healer in a BG. Blizz really needs to go back to the drawing board and completely rework healing in pvp.