I agree it is very difficult, but I'd bet teams will get better at it if they haven't already. Stewart was considered the #4 prospect so it's hard to fault the Twins for taking him. From my understanding, Stewart doesn't have the velocity that was expected, and perhaps has actually even decreased since he was a teenager. Additionally his slider which was expected to be a plus pitch is barely usable to below average depending on the various reports now. I have to think some team is going to develop some kind of analytical model that is going to be able to better predict velocity changes, development of secondary pitches and perhaps even likelihood of injury based on age, body type, innings pitched and what kind of mechanical changes the team will require. It would be difficult surely but I seem to read about a dozen or so new technological advances more mind-blowing than that weekly.