So far, I've found forcing a complete reroll is actually more balanced than just one pair of die. This is because you only get 1 more Damage (at best) while using MRD along with this concept. However, by rerolling all of them, you could end up with less Damage than your initial roll.
And of course, the same thing could be applied to Float Like a Butterfly, too. Having a chance to only reduce Damage by 1 instead of more, at the risk of having all the Damage hit, is rather anemic.
And this is from someone who Floated a series of Attacks from 1 Structure Damage to 3.