I don't care what any GM say's it is truely a crap shoot when it comes to drafting rookies that become 'superstars' no one knows how good players can become with a few exceptions (Lebron, AD, Shaq, Kareem, Wilt ect.) Ainge would have know he had intangibles which is code for educated guessing. If you look at the history of Superstars in the NBA there were many doubts about them as players throughout their career.
Jordan- thought to be only a scorer and was almost traded multiple times
Barkley- too small, lazy & fat
Bryant- worked out for Boston (including others) & decided not to draft him
Curry- too small, tweener, not a playmaker ect.
Draymond- was thought he could be a solid bench player
Harden- great 6th man but thats it
Durant- too skinny
Leonard- Pop stated he didn't really want to trade George Hill for him