Furthermore, I think that we can all agree that a big cushy heel of a trainer will allow for a runner to overextend and use their heel as a crashpad, while that is not true for someone in a thin flat or unshod.
I think most people will learn not to use their heel as a "crashpad" just by doing double digit milage in flats or spikes, and anyone who uses flats/spikes for speed work easily gets double digits out of them. And again, I simply don't agree that you have to do all of your miles in flats. There is no evidence that supports this.
2) I'm going to have to call my favourite anthropologist for some concrete data in terms of time spent on the feet, because I say that their time on the feet is comparable, you say no
Even if they did an average of 2 hours running a day (so that means 730/year -- it's not good enough that they do 2hrs on a paritcular day), it still is not the same as training for a distance race, and you are still incorrect to infer that the unstructured running of a hunter-gatherer is comparable to an artificial athletic regimen that is imposed for the purpose of competing in a distance event. I bet that the hunter-gatherers would experience much higher injury rates if they all commenced a full-blown 10k training program, complete with a goal race and an incentive system. Again, I'm not disputing that the puma H streets are fine if you want to move to a remote area and take up hunter-gathering. But that's not the goal of most of the posters on this board.