I agree. The max effort thing is a big deal. Guys back in the day didn't max out every pitch. Nolan Ryan could throw 103+, but he only did that when he needed to ramp it up, a few times a game. It wasn't every fastball he threw. Ditto most successful pitchers back then.
Too much breaking stuff too early as well. A kid with the talent to make it to the majors doesn't need a breaking ball as a 12 year old, and he sure as heck doesn't need a slider as high schooler. Plus to try and throw that hard, kids develop all sorts of bad fundamentals. Ryan was a scientific miracle, but he also had flawless mechanics. You what happens to the guys who can actually hit those kids a bit? They are the guys who get drafted.
This is a huge reason.