I have vivid memories of Mo chewing out Duncan for a mistake on the court. Mo has the personality to boss people around, it's a lot harder for Duncan. Also, Duncan gets down on himself and that's a bad trait for a court leader. So I see Mo as a court leader before Duncan, although there's certainly important things that Duncan will do as an experienced senior, same for MAAR.
Simmons is a different situation. As a point guard and assist man, he sets up the offense. But it's his first year at UM and he doesn't know the system or the personalities on the team. So he may not be the guy to pick up the team when things are going poorly.