I think you forget some important point about Healing Paladin in PvP.
Paladin is probably the best healer and support class for alliance in PvP ( even both side really ) for some obvious reasons :
- Low cost magic / poison dispel, and has a good mana sustain.
- Bubulle 12 s of full healing spam no matter how bad the situation is.
- Rogue cant kill them in a few sec ( unlike a priest or a druid in normal form ). Even more if they are reckbomb heal spec ( Holy + reckbomb ). Paladin > Rogue.
- Priest get raped alliance side because they get fully purged by shaman or shadow priest, and they cant really escape.
- Druid see all their hot purged most of the time ( Shaman again ), they are still best flag carrier for WSG and got the best Instant heals in the game ( they are pretty decent in CC aswell, stun root silence ), but not as helpfull as a paladin in a group fight. Druid really shines in skirmish.
- 2 Paladin is an OP combo with dispel control of each other combined with 2 Blessing of sacrifice. Almost unmanageable if played well.
But still paladin got some weakness like fear, Magic damage, Warlock ( curse of tongue + fear ), kicks, silence.
A reckbomb heal paladin with 200 shadow resist is probably the most pain in the ass that you could ever encounter.
So my opinion is that Paladin is probably one of the best PvP healer in the game, and Shaman is mostly an hybrid damage / healer with an amazing burst. They both reflect their side : Horde = aggressive, Alliance = defensive
Sry for Ret paladin, but unless you have a good gear, you are way more usefull as a healer.
Note : And i didnt talk about the wombo combo warrior / pal.