JS Fan, the Hawks coaching staff is from the old school. Rookies generally don't get to showcase themselves very often. Josh would not be playing if there was a vet who could adequately replace him.
The offense is clearly designed for Al and Walker, not Josh. He is simply playing within the structure outlined by the coaching staff. If he's called upon to score more, I'm sure you will see his numbers increase.
I'm sure your a true student of the game but your comparisons to JR Smith and other rookies are really offbase.
JR Smith plays with one of the best penatrators in the league in BD. BD drives the lane, the defense collapses and JR is left with a wide open jump shot. I'd bet you would score 20 a game if all you had to do was catch and shoot uncontested. Unfortunately, Josh doesn't have the luxury of playing with BD. I'm sure you've also noticed that he is tasked with the leak out player in transition situations making it dificult for him to play below the 3 point line, which reduces the chance for higher percentage scoring situations.
Luol Deng is playing on a much younger team with no one who demands the ball as much as Walker or Harrington. Who's the go to guy on the Bulls? They don't have one. It's much easier to score when you have the green light to shoot the ball.
I agree with you in that Josh has not done anything that merits highlight reel consideration, however he is not doing as bad as you've lead on to believe. Your expectations of granduer may not fit in with the team philosophy.
Remember we are in the preseason. Everyone on this team is trying to establish their roles. As a rookie sometimes you have to remain humble, bite your lip and wait your turn.