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I agree that Kawhi can be a team leader on the field. He showed it many times in matches of the regular season, as well as in the finals - in San Antonio beating LBJ or later in Raptors. However, Kawhi lacks the expression and charisma that a leader should have. The leader should be able to raise the team's morale not only by playing well, but sometimes also by some kind of behavior, I don't know, big dunk or a some gesture towards the fans. A bit of the character of a showman who can inspire the whole arena. Kawhi doesn't have it or shows it extremely rarely.
We might not seeing him talking to his teammates when he is playing, but as we see, whatever teams Leonard plays with, the team will improve and become a playoff contender and even a championship contender, what he did with the Toronto Raptors was a big achievement already, he gave the Raptors their first championship in their history (correct me if I'm wrong) and we even underestimate the Raptors with Leonard but Leonard proved us wrong.
The Raptors are undeniably having a good coach as they are still a contender now, but good them they have Leonard who listened and respect his coach so there's no division within the team.
Coach job is to design the play and players will follow whether you are a star or not.