Normalizing over an encounter doesn't help cutting edge mythic progression. When I needed to blow shit up on demand during mythic archie progress last august I didn't have the option to rely on hoping that it normalized over the encounter when I needed to burst specific adds down in seconds or we wiped.
It's pretty much exactly like TFB, if I don't get the high roll then my tiny damage is meaningless and we wipe, if I do get it we kill the target.