I have a feeling that the developers have a hard time balancing healers for PVP combat. How should healers be killed in PVP? Should we run out of mana eventually, or is a bursty switch the only answer? Can the focused efforts of a single DPSer be enough to topple us, or should it take two players to finish us off? Trying to balance all of these elements for four different classes with five different healing trees is a challenge by any measure. Every organized PVP encounter revolves around the healers involved, especially in the golden bracket of 3v3.
Prior to patch 4.2, teams loved seeing a holy paladin across the arena from them, as holy paladins weren't exactly amazing at 3v3 matches in the first few months of Cataclysm. We have a few key weaknesses, notably our lack of any long-term crowd control like Hex and our lone school of magic, holy, which leaves us defenseless when interrupted. We weren't completely ineffective in arenas before patch 4.2, but we also weren't breaking any records or winning any #1 Healer trophies.