Squad heal here have only one problem - long cooldown. But people can survive easy 3sec without healing If you see that someone is dying and squad heal still in cooldown - stream of rejuvection,as you already mentioned.In GV purify isn`t needed much.
I've double cliented a lvl 130 cleric with full 130 gear. It worked out fine and I didn't die once. Then again, we did have a couple of 150s in squad too Anywho at 130+ you should be able to tank a handful of mobs just as long as your squad does their job right and actually takes aggro.