I agree, athleticism isn't everything, but it is a huge part of what determines the ceiling a player can have.

MacClung is a player:

3 star prospect out of high school
Averaged 42 ppg his senior year (breaking the state career and single-season scoring records held by Allen Iverson)
Scored 47 points in the state championship game (breaking the championship game record held by JJ Redick)
Started 29 games as a freshman at Georgetown and earned Big East all-freshman honors

He has things to work on as well. He needs to take better shots and not force the action as much but his ceiling is extremely high and he could be a game changer at PG.

This isn't a shot at past BYU guards. The fact is that a player of his caliber that can play above the rim from the point guard position does not come along that often for any school, let alone at BYU.