While the specifics of that situation are debatable and ultimately probably of little importance to most of us, it does raise a couple interesting questions about what qualifies as leadership. Kawhi is indisputably one of the top basketball players in the world. He is also famously reserved.
Being an outstanding performer is often associated with being a leader. Being introverted is often seen as detriment to leadership. But in fact, neither is necessarily true.
Quiet people can be phenomenal leaders. They have advantages of observation and listening that extroverts struggle to accomplish. The ability to think before speaking and acting avoids impulsive errors and stability builds trust. In fact, some of the most powerful visionaries and communicators I know are strongly introverted in most settings.
Personality characteristics and profiles can be useful tools to understand and work effectively with others but they are inappropriate for deciding whether someone is or is not capable of leading.
In a similar way, the ability to perform at a high, or even elite levels is no reliable predictor of leadership potential. While there is certainly a tendency for us to look towards achievers for their example and best practices; the skills of leadership are often quite different from those of technical or individual excellence. It is often those who have less innate ability who have the capacity to equip others to succeed.
The best players are not often the best coaches.
So I really don’t know if Kawhi Leonard is a leader on his team. But I know that his personality and performance alone don’t tell us enough to figure out the answer.