Even 2-3 shots placed on center mass could have knocked the gun man out of the fight. Just because the round doesn’t pentrate the body armor doesn’t mean the kinetic energy is gone. The physical trauma enacted on the body from the rapid deceleration of the round can break ribs and cause internal bleeding. I bet some heavy internal hemoraging or a collapsed lung would have slowed him down quite a bit. Even if one armed citizen could have stopped him half way through the rampage it would still haven’t ment lifes saved.