The benefits of protein are historically documented by all the great bodybuilders. Nothing new here. Mainstream is always behind the freaks who dare to go against "science".
Which is amusing, because in this context the bodybuilders are fundamentally doing science. They have experiments (aka, exercise and eating regiments) that, as I understand it, are repeatable, and consistently produce the desired outcome, at least in terms of sculpted muscle and body fat.
This article kind of addresses that. It mentions that this has been known but says it is unclear whether these high protein diets are effective for groups outside of your traditional, male bodybuilder.