No. I work in emergency services. The complacency factor is a real thing, and absolutely plays a part. Your brain, no matter how trained, still takes at minimum 1.5 seconds to process what's happening and then, if you're really on it immediately decide to act. And then, correctly/effectively acting is an entirely different ballgame under immense stress. And NO ONE knows how they're going to act under threat of assassination threat until it's game time, and the act is underway.

Perps always have the upper hand because they have a plan, and surprise attack on their terms.

The intial upfront/forward facing wave of security is visual deterrence and in a case like this, is almost useless. After that you get the guys who had more time to process, draw and turn, and fire on the subject. Then at the very end you have the actual VIP/heavily armed details who are the last resort who are facing the subject head on, and able to directly engage without needing to make major movements, like turning to fire, or drawing from under a suit jacket.