The thing is people do what provides results. Saying to throw out a routine that is based on progressive overload is ridiculous because of the fact that it has provided results to so many people.
What matters in weightlifting/bodybuilding is real-world results that have been seen and experienced. As for the two guys you cite as sources, degrees mean nothing, how many high caliber athletes or bodybuilders have they cpached/trained? How many average people have they trained to significant gains? Have they ever lifted a weight and made an ounce of progress? Results matter, not theories and experiments and hypotheses.
People aren't telling bodybuilders to train like a football player, what happened is that people used this routine, saw it grew muscle, saw that people plugging away in a gym doing cable flyes, and concentration curls, and emulating what they saw on the movie 'Pumping Iron', and getting 'pumps', and weren't using ridiculous amounts of steroids were not growing any muscle.....How many times do bodybuilders talk about 'muscle maturity' acting like you need to be 38 years old with 25 years training to look thick and dense.....if you'd build up your weight over the same sets and reps on basic, compound, multi-joint exercises, and eat enough, you get thick. I have seen 15 year old kids with 'muscle maturity' simply because they train correctly.
Research and studies are worthless without real world results on the average person.
Another point you miss is this......5x5 is progressive overload. the most important thing is NOT that it is 5 sets of 5 reps.....hell, it is supposed to be 4-6 sets of 4-6 reps, but 5x5 was simpler. This can be 3x12 or 4x8 or 5x10....the sets and reps are secondary to the issue of progressive resistance.
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