I don’t think that tough training is suitable for all people. In my example, my military training was minimal, I went to a two week boot camp, was promoted to E-4 and spent a couple years in schools. I then spent 12 years as a pretty good Petty Officer, without having to endure the sever training that some my peers received. If I had been abused in boot camp or in other training I suspect that I would have just quit and headed off to the university to complete my training.
I know football and basketball coaches that get the best out of their player without resorting to abuse because they lead by example rather than force. I would guess that you would get faster results if you coached with abuse and fear but I believe that you longer lasting results if you lead in a positive and supporting way.
Maybe you need really rough training to be in something like Special Forces but you can twist a person in a way that they aren’t likely to be happy or useful outside a military environment.