The problem is the prospect observer effect—once people notice that players who "hold their own" at a young age tend to become good prospects, the unquantifiable thing that observation was measuring is changed forever. That calculus—involving the team noticing a teenager playing far enough over his peers, and being sure enough of his skill to put him in a league that will test him instead of one he'll dominate, before he gets moved up to full-season ball—is no longer valid once a team makes it part of the philosophy.