This is a huge jump from the problems associated with his jump shot. What exactly do you mean by poor decision making, and how did you arrive at this conclusion?
I would argue that it is his amazing basketball IQ that is what separates Ball, who just turned 20, from the vast majority of players, regardless of their age.
As of this writing, his assist to turnover ratio is 2.66, which is better than Simmons, Harden, Westbrook, Lebron, Curry and Durant. I would say making the right pass instead of throwing the ball away has a very high correlation with good decision making.
Also, his understanding of team defense concepts and timing when he double teams an opponent in the paint result in him being #3 in the NBA among all guards in blocked shots.
Simmons is fantastic, and will probably win ROY honors, but he hasn’t worn a target on his back from day one, like Ball.
The reason Simmons is scoring has nothing to do with his shooting ability (he avoids jump shots like the plague); it is because he’s four inches taller and forty pounds heavier than Ball, so he is able to finish at the rim.