or that in actual fact most people with average intel' could probably manage it given the opportunity and a patient instructor
Over the last few years I have watched my son go through the military training process, wondering at the same time whether I could have made it myself. I suspect that, given enough time, I probably could but the one thing that military training does not normally give you is time. If you don't get it after one lesson or so, you're chopped. There probably is a small percentage of people who could learn at the pace required by the military. In fact, the number of students on my son's course who made it to the end was quite small, three I believe.
It's just a pity that they have to spread it over such a long time.