In 2014, Marcus Smart measured 6'-2" without shoes, 6'-3.25" with, 227 lbs, 6'-9.25" wingspan.
In 2009 (is he really that old) Curry measured 6'-2" without shoes, 6'-3.5" with, 181 lbs, 6'-3.5" wingspan.
Not sure what this has to do with Smart's development but seems like a pretty easy argument to settle.
I think durability has been the biggest issue in Smart's development. I don't think all the other stuff matters so much. I remember Smart in the first summer league games. He was horrible but he improved rapidly until he got hurt. I don't ever remember seeing a player improve so much from summer league to regular games. It was like every game he figured out something and made it part of his game.
Durability is my biggest concern with Smart but close behind is his lack of shooting touch. This is the key area of his game that has not improved much. I think he can get points but to fulfill his full potential, he just plain needs to shoot better. Staying on the court will help. I don't think it matters what court role he plays or who he plays with though. Shooting is shooting. He needs to get better.
Those long arms are great for defense and rebounding but Curry seems to be doing much better shooting with short arms. I guess the answer is we need to shrink Marcus's arms.