What point do you think the play may be attempting to make about leadership in a democracy?

Juror 8 is a strong leader, but the important thing is that he helps all jurors say what needs to be said. In a true democracy, everyone has a vote, regardless of background, ethnicity, or previous experience with the legal system. Juror 8 helps everyone participate until some kind of decision is made. That may well be the true definition of leadership.