OK My understanding was other officers were in immediate pursuit from the car chase and he would not have been able to go room to room. So whether SRO engaged or not made little difference in outcome. However, I forgot about dropped ammo bag, so if he did not have enough ammo to kill all kids in room, then in that case the engagement saved the not shot kids in that room for sure.It lessened the number of children killed. After being engaged by the SRO, the shooter holed up in one classroom and "only" shot the kids in there. If the SRO hadn't engaged (causing the shooter to drop his bag containing more ammo), the shooter likely would have gone from classroom to classroom shooting up all the kids.
NoI think you are jumping to conclusions.