They know what they are doing... they are nerfing dps gain from intentional taking damage you are not supposed to take. In normal conditions you ll almost never reach vengeance cap and it ll have minimal impact on those tanks - they ll most likely still be in top5 in most of the encounters.
It ll no longer be viable tactic to stack Anima Ring on your paladin tank or solo tank whole fight despite stacking debuffs. It is good change...