Smart is a guy you're always going to want on your side. Marcus is a young warrior. Warrior's have men/teammates that follow them, men that emulate them. They glue the team together by how they respond. (Draymond Green is one for Golden State.)
Every team has guy's they look to when things get tough. Marcus takes the charges, gives his body up, he hurts people when he defends them, he never stops trying to get an advantage. He actually annoys people he defends. He turns Celtic team defenders up a notch.
But, he needs to get his offensive value to rise. Or he will not get the minutes he needs to accomplish what he can. Some of us are betting he will.