Second the NOPE
I was a Combat medic (as in I was on the line, not changing bed pans)
I knew of two good medics, when it came time to perform under fire (actually by then the firing had stopped) the failed, completely flustered.
In train they were great, they knew their stuff, the were wonderful on sickcall (clinic) but under stress they fell flat.
That said, I think training can help, you go through a full up "Aw, ****" brown drawers sequence, where the person going in KNOWS NOTHING of what is to happen. Then you analize it, you walk it through step by step, then run through it.
And then you throw them into something completely different and see which way they jump, eventually you CAN train the jump out of them.
OK, and here is the BUT
Alot of the hesitation and uncertainy comes from having to cycle from 'everything is all right' to 'I'm under attack'
Take a Kung Fu movie analogy, Kung Fu master gets attack taking a walk and smelling the flowers he reacts, he doesn't have to spin up in a OODA loop, he has trained himself to the point where he has the Heuristics and reactions to short cut conscious decisions.
when he's attacked his mind recognizes "under attack" and reacts accordingly
where a student may know ALL the same moves as the master
but when attacked his though process is much longer
first having to come to realize it IS an attack (and get past denial- BIG POINT)
Then he has to remember what to do.
I think most people fall into the second category
and most people will fall into DENIAL and fail to react to the threat in a timely manner
no matter what their range skill, they may be a perfect shot, may have a blazing quick draw. If they don't train themselves and ready their mind to fight back, they won't or they will have a major delay deciding to start to fight back.
Read true crime, Sam I think you linked the BTK confession, every victim fought back, almost every victim either gave in or failed to react to the initial attack. The true struggle didn't happen until they realized they were going to die. Those that fought back immediately where the victims that managed to escape or survive.