Throwing my 2-cents in, I think there were fundamentally two factors that contributed to the disaster.
1st: as so clearly attested in earlier posts, there was every reason to believe these were really, REALLY bad guys. Bunching all the cars into a tight ball just seems like a bad plan. Dropping one car back with your average AR15 would have changed the dynamics considerably.
2nd: these bad guys were COMMITTED to the fight. I've studied the autopsy photos at length and see prime examples of "lethal" hits - one striking the cheek and driving into the skull, which failed to immediately incapacitate.
I think the big lesson here is one we can all reference when discussions come up re "excessive" force of heavy calibers, etc - if faced with a foe who is determined as these two scumbags were, there is no amount of pain or superficial injury in the world that will stop them in a timely manner. They were not jacked on PCP, just pumped on pure adrenaline and nastiness. That has carried soldiers through incomprehensible battles at war, and sadly will carry many a perp through a "textbook" defensive effort.
Shoot big, effective bullets, and shoot as fast and as accurately as you can until the bad guy goes down and stays down.