I think you are totally right and as you said you have been there and got the tee shirt. Dr. Ignatius Piaza who owns front sight says that in a live fire situation you will function at about 70% of the best level of accuracy you ever managed to achieve.
https://www.youtube.com/watch?v=KmhGYB4NdYc
That’s the link to the shootout in Unforgiven on YouTube. The thing to note is the depiction of the deputies and posse guys shooting holes in the bar, shooting into the floor, and the inability to realize William Munney (Clint) was down to his last bullet although there were still maybe eight of them standing.
As to the 70 percent functionality in a shootout. I doubt that for the average person. Law Enforcement and others who get specialized training about shooting judgments, maybe. The average soul? No.
The firefights I’ve seen always began the same way. Huge, wild expenditure of ammunition fired blindly. (Works, too! The bad guy is scared, too.) As the engagement settles into a prolonged battle, you can recover your senses and think, aim, see, and shoot straight.
Best we can do is practice shooting. Get familiar with our weapons. And visualize the discipline again and again that it will require in the first seconds of a fight.