My only real experience healing a dps geared tank is from a long while back. It was with a FC group trying to clear Titan HM for the first time. The MT died and the OT wearing dps gear was one shot by the next mountain buster despite having cooldowns up. He was a PLD.

I'm sure in content like t4 it isn't much of a difference with how geared out people are now, but if my tank were eating plummets with little parry I'm certain I'd notice this.