I understand that idea. It could be an interesting option to Purify more overall, but you already Stagger 75%-85% of Physical damage taken which is a big portion of that initial hit. What could be interesting is merging that idea into a defensive CD such as Fort Brew to make it 100% Stagger for that duration (it’s already like that but not 100% stagger, not sure the exact number in SL tho).
Also, having both short duration 95%-100% stagger for 3-4sec + Purifying Brew would most certainly lead to imbalance.
The point of damage mitigation is to reduce stress on your healer and therefore ‘‘make your healers job easier’’