Cribbing really is stress-induced, as are pretty much all stereotypies, and then it really matters if the genetics are there to manifest as the behavior. That’s not disputed. But not enough turnout (remember, this guy is out 9 hours a day), is not he the only cause.
By dismissing the idea that stress can’t originate in a dietary deficiency (it absolutely can), only by lack of turnout in this situation, you’re doing the same thing as those you’re arguing aren’t taking management seriously.
So you have no idea how to manage a horse in any sort of stalled situation, but you’re ok telling someone they’re doing it wrong because you don’t do it that way?
Imagine how many horses have gotten in trouble because of illness or injury that required stall rest, but had a meltdown because their people didn’t believe in stalling and never taught them they can not just survive, but be content, for some period of time in one.