to the differences between NBA and NCCA ball, could be a good baseline or ceiling for a players ability to make or not make the leap.

There is opportunity cost in one year at school both financially and in ability to develop. If he thought he could best improve his game by staying at the Y then I am sure he would have.

There are plenty of guys who have done the four year thing and it didn't pan out, Haws, Plaisted and Davies are a few that come to mind.
The one point where I agree with you is that he would have had more eyes on him in the NCAA rather than in euroleague. There are hundreds of great NCAA kids out there every year, but there are only dozens of spots in the NBA. The NBA requires athleticism, something that is in short supply in Provo.