TexKSAH Respectfully, you're conflating a few things here. First, let's not consider buffs for a second. Shaman heals are 30% less efficient than a cleric, but a mob once slowed does half dmg. If mobs arrived pre-slowed, it'd be a net win, but otherwise it's basically a tie.
Now toss buffs back into the mix. If you can tie a cleric on healing AND apply all those buffs that massively increase dmg...why would anyone choose a cleric? They wouldn't ... which is why pre-rework, shamans were significantly preferred over other priests.
Since TTK is so low, the change to slow is beneficial to shamans ... it lasts less time, but costs proportionally less mana. That means it pays off on mobs that die fast, at the small tradeoff that you cast more often.
Finally, I'll note that shaman can heal in nearly all the content out there, whereas there many camps that a druid cannot heal ... not unless they have enchanter slow and mana regen to help them out. I know you want to make this all about shaman v. cleric, but there are three different priest classes.
