I wouldnt say, that pallys not good for healing MT. I tried priest shamy and pally, and with pally if i have to heal only the tank, i easily did it. I think priest, is for healing the others. The why is easy: pallys are the fastest healer, with flash of light, they can hold the MT's life above 50%, and they have a nice amount of mana, and flash of light is cheap, so they keep up this for a long time. And for the resto shammy: its a really good healer, and they have enough mana. If u say, they dont, then u didnt see any well geared shammy.