Pretty much true in all the team sports except sometimes basketball.

The foundation roles like pitching staff, O and D lines in football require development and have high rates of failure because you can't tell what a 17 yo is going to be when he's 20. Physical and mental development is the key to those roles.

Other than the occasional phenom, you build a program to develop them and expect some portion to contribute as rSo/Jr. Especially pitchers. So many are massively over-worked and have terrible mechanics and habits in HS and all the development leagues they play in, a year of rest, conditioning, physical maturing and being taught how to prepare and take care of themselves at this level can be the difference between a top performer for 3 years and a kid who is always hurt and everyone looks back when he leaves and says, what if....