Right. We experiment (i.e. "trial and error"). That's is how we find out what DOESN'T work. 3 times a week didn't work for me. That is what I am pointing out. My best and fastest gains came from training each bodypart once a week. Keep in mind, it is not just about training. It has to do with what the CNS can tolerate and the connective tissue can handle. Obviously some people can handle a lot more volume then other people. If they are on gear and have fantastic genetics this "correct volume" increases greatly.
Surely you are NOT advocating that EVERYONE train the same way? i.e 3 times a week? This would mean that you think it is the best way to train, and not a single 'guru' or bodybuilder to my knowledge (with the exception of Mike Mentzer) has ever claimed that they "know the best way to train".
Taking your logic about how training more often is better, then we should be all training six days a week. Because if three is better than one why is 4 not better than three, and five not better than 4? See where I am heading here? Why is 3 the magic number? Why not 1 or 2 or 4 or 5 or 6 or 7?