Of course, the other issue is that it's a bit of a lottery at that age.
Not saying we couldn't do better, but there are many players who shine at an early age then disappear while others do the exact opposite. We have Thomas because Celtic thought he was too small, and guys like McHugh and Moore, who scored goals for fun in the U20s for a couple of seasons, never quite managed to make the step up.
I'm sure if Erwin was still with us, he'd be on that list.