Agree with what you discuss above. What I would like to bring up is cover and concealment. There was no cover available, and very little concealment. However, the first armed responder appeared to stand up and present himself to the shooter, and then start his draw. His draw was obvious and slow, giving the time for the shooter to shift his attention and shotgun from the usher to the first armed responder and fire. By standing first, then reaching for his pistol, he appeared to draw the shooters attention to him. The shooter’s shotgun was already out, while the first armed responder had to perform his full draw cycle while under the direct attention of the shooter.
Watching the video repeatedly, I wish the first armed responder had performed his draw cycle while seated, and partially concealed by the pew in front of him. He would not have drawn the shooters attention to himself until later, saving himself one or several critical seconds. The shooter has his attention initially focused on the usher. it appears that If the first armed responder had drawn and presentEd from partial concealment, then risen as necessary for a clear avenue of fire, he might have created a more advantageous outcome.