from what ive seen so far wingspan is the greatest indicator of whether or not someone has the potential to be a star
but those with average wingspans can at least become contributors like jj barea
Its not the greatest indicator but so important. The greatest indicator to me is reaction time or concept that first to the ball wins. And when you have long arms you are often first to the ball. But you can have length and react slowly to plays. That's one of the reasons I knew a guy like Jason Thompson was a scrub before it was made official and he washed out of the league in the "prime years" of his career. He was a half step late on every play because he just did not have instincts to go after it.
It's also one of the reasons I LOVE players like Buddy Hield and Kris Dunn before the draft. Their reaction time is outstanding. While Buddy is known for his ability to shoot and create, he does a tremendous job in transition, a function of reaction time to change in team possession. Dunn also reacts well to get through picks anticipate where his opponent is headed to cut him off at the pass.
If I were an NBA scout, I would look to size and speed and length as first indicator, and then reaction time as an intangible within context of tangibles. As an aside this is something that could hold back Willie from developing into a ferocious presence in the paint. His reaction time and anticipation the ball is poor as a rebounder (better as a shot blocker) despite his extraordinary length. I am not sure how much he can improve in this regard, since the instinct to go after the ball and anticipate is often there or it is not.
Getting stronger in his base will help him hold his ground and clean the glass but he needs to do a better job of going and getting it instead of standing there before it is too late. 4-5 times in the first summer game he missed rebounds he could (should) have had.