as far as his shot goes. I haven't watched his form or anything like that. but from what I've seen his major problem imo is something that just about every rookie suffers from - "shot selection".
It's more than just shot selection - though smart shot selection could certainly improve his numbers tremendously.
He has an actual, very visible flaw in his shooting form, especially as he gets farther from the basket. Instead of bending with his knees and keeping his spine vertical throughout the shot, he "clamshells" -- bends forward at the waist before rising into the shot. This means his spine is going backwards and forwards as he rises through the shot.
He's been doing this for the three years I've seen him on the national stage and the results are his outside shooting is what it is. He was a 29% 3PT shooter each year in college and he's currently a 29% 3PT shooter in the NBA.
I've seen no visible attempt to address this flaw in his form so far in his limited NBA career.
This is where comparisons to Billups deviate. Billups also struggled to shoot when he came into the NBA, but that looks more like rookie jitters in hindsight. Billups was a 38.2% 3PT shooter in college. (Both players took a LOT of 3PT shots in college.)
Shot selection could be the answer, if they can't fix his form. There is no fundamental law of the universe that says Marcus Smart HAS to be a good 3PT shooter in order to be a good NBA basketball player. He may never be a good 3PT shooter. But he is a decent FT shooter and short-mid jump shooter and in college showed the ability to get to the hoop and the FT line.
Stevens needs to focus Marcus on doing those things that he does well and stop having him do those things that he doesn't.
In the NBA, the talent level is just too extreme to be trying to do things you are not excellent at.