IT would be a nice addition to any team in the league...coming off the bench. He's a nice spark, because he is instant points. A pace changer, the game quickens up when he's inserted, and that has to be adjusted to by opposing teams.
As great as a defender as Marcus Smart is, he's really not a naturally gifted offensive player, he's quite immature. Besides taking off balance 2's, and generally some poor shots, Marcus tries to play like he's still in college, he has yet to figure he needs to add finesse to his game. He's just not a stand still explosive leaper. He needs a floater, a jump hook, a fall away. he needs to master the up fake, and get the defender off balance and in the air. He hasn't figured out just how big, strong, and long the NBA is yet.
Only one way for him to learn, and that's to play. Give him enough rope to see if he learns... or hangs himself.