I don't know about recent studies, as it's been years since I read any fitness studies/papers. Though I concur with the thread statement based on some personal observations. I spent about a decade working out in Navy/USMC gyms with a variety of strong service members (young and old) and veteran gym rats. Saw 100s of guys come and go, as I was in the area permanently, and most of the men were typically shipped off after a several months, to be followed by a new crew. Met/worked out with various proponents: Leg-press only guys. (45 degree) Powerlifters (low-bar back squat /thick belt/knee wraps/flat shoes/) Weightlifters (front squats w/weightlifting shoes, sometimes high-bar back squat). Bodybuilders (variety of the above) The rep schemes varied as well, 5x5, 3x5, 1x20, 10x10, etc. From what I saw, generally, many of the hardcore powerlifting guys (squat) were absolute monsters. The weightlifters (squat) had enviable physiques and just looked overall athletic, and quite a few of the leg-press only crew were big upper body guys (disproportionate to their legs). I recall at times there would be pissing contests between the leg press guys and the squat rats over who had the stronger legs. Mini-contests and stuff. From what I recall, the squat guys could get into a leg press machine and hold their own on day 1, but the leg press guys were hard-pressed to even walk out a heavy weight under a loaded barbell, let alone drop to parallel. Obviously, it takes coordination to do 2-3 backward steps and perform a proper free-weight squat. Not something you learn in a single day, or master in a single week/month. Another note, I remember one guy who would load the LP up with every damn 45 in the gym until there was no room left on the machine, and then do several reps. He would always have an audience. (maybe cuz no one else could find a spare plate).
Interesting observation. But you also need to keep in mind the possibility that people with a certain type of physique are naturally drawn to certain forms of activity. For example, people don't take up swimming because they want a swimmer's physique. (And if they do, then many find disappointment.) Rather, people with the makings of a swimmer's physique are drawn to swimming because they are naturally good at it. And so, I'm not suggesting that exercise choice is not important and has no effect. Far from it. Rather, I think it's important not to assume that all else is otherwise necessarily equal when you see such disparity in outcomes.
A well designed leg press and one that fits your body segments beats squats all to hell for thigh & hip development. WELL DESIGNED, ie. Many are not! The spinal muscles, work them separately to in another machine thats fits well.