Thanks for posting the video. The first thing I noticed was the first guy stayed out in the open. I've told my wife that if she ever has to shoot, she should get behind something and stay low. 
I agree that cover is the alpha and Omega of such situations..
But I find it hard to judge from here..
What if the only "cover" available are the other ppl in the church... it certainly seemed like that for some of the responding Deacons.
Also as sheepdogs putting down the bad guy has to be priority for the Deacons.
For this they good need line of sight to the target.
I would also hesitate in this fire geometry taking a knee and then as a result not seeing the threat and being unable to service him.. while he kills in his corner of the church.
It may appear that in situations like these ( full church) rather than fire and movement (which as u all know I am usually a big proponent of) pulling the pistol then engaging the shooter in the quickest manner available (and as a result accepting the risk of scant attention paid to cover) may be the way to go...
