Your paladin gearing haste has nothing to do with failing on tortos, haste is fantastic for aoe tanking, I one tank tortos as most paladins do with haste step up, it was more likely your healers failed at keeping his shield topped up.
Anyways on this topic, stupid nerf, pointless and it will actually hurt fights where you can easily gain vengeance, i mean god look at horidon, wth are we meant to do on the enrage when we are suddenly getting half the vengeance, there goes our active mitigation..
Seriously what does this stop people doing 1 Tanking Council or Megaera, its like a cheap bandage, lets just fuck over the tanks actually having fun and doing there job properly, seriously its not like people are standing there trying to take more damage on heroic encounters.