As I think about it I think what they could add is basically… re-add hyper-armor. 
Add a defense check to stagger - if a crappy low-level pissant attacks a high-level opponent with high defense (armor factor, armor quality, agility) then the stagger should not happen.
The simple thing to do is admit they were wrong and revert Ch2’s reduction of hyper-armor. But in the best of circumstances it takes them about 2 years to admit they were wrong, so why not keep on pretending they have any hint of intelligence and keep “refining” combat with some extra code that runs on every weapon swing to do a defense check to negate stagger.