[Sarinpa1]

You really should try doing that in actual combat. If we go, let's say 2v2. One side has this healer and one side doesn't. You'll see how quickly the side without healer gets fucked over and ded. It's not like both the priest and the one they're healing is just standing around. And interference is rarely an option unless you've the specific classes.

And as stated in the OP, PvE is utterly trivialized with this.