Everyone responds differently under duress. Some step up, some freeze.
The argument is effectively moot if you hire people that neither have the proven experience in dealing with emergencies, in an airplane or not...your simply gambling that the first time it comes up, with you in the back, that they will step up should that event come to bear.
My personal experience is that some people look to challenge themselves under stress, others avoid those situations. Those that challenge themselves are the ones better 'trained' to deal with these events mentally.
As far as how far or how willing a person reverts to 'crawling into a corner in the fetal position' can simply be tested by putting them in situations where they are tested for that. Some will fight to the end, some will not.