30 seconds of covering behind a seat?..interesting
Body armor isn’t a invinsibilty shield and the fact that your idea of tactics is assessing an active shooter for half a minute before even drawing your gun, or that a person is impervious to pain and unstoppable because they have a bulletproof vest on leads me to realise that your hollywood outlook on an appropriate and realistic reaction for this and other scenarios is not even worth getting into.
Person with a gun in the crowd > none
However, even how off base your idea of the 30 second assessment, and COD juggernaught body armor idea is I will admit its a difficult situation and even if someone had a gun they would have to be in the right place, with the right training to make a difference.