Superman Isn't the Only Justice League Hero Who Deserves to Lead.
Superman has always been an obvious option to serve as the Justice League's captain because he is DC Comics' original and most well-known superhero, but the Martian Manhunter might be a better choice.
It makes fitting that Superman would serve as their leader as the Justice League and teams like it were created to be a bulwark for the inhabitants of Earth.
Together, they have saved countless lives and, with Superman's help, have helped to make Earth a safe place for humanity to live. However, Kal-El is not the only excellent leader.
J'onn J'onzz, a.k.a. the Martian Manhunter, is the ideal choice for leadership because he is the inspiration behind many Justice League teams. The Martian Manhunter is an accomplished leader who founded many of these teams after the original Justice League was disbanded. He oversaw the Justice League of America, Justice League of International, and Justice League Task Force.
Batman ceded his leadership role to J'onn J'onzz because he saw that the Martian would protect everyone on Earth rather than just one nation and would utilise his power of leadership to do it.
J'onn was the only person Batman felt he didn't need to "coddle" in the early phases of the Justice League International because of his cool head. Due to his earlier teamwork expertise, The Martian Manhunter was able to make the proper choices
eventually take charge of the sole Justice League on Earth for a period. He developed ties with all the nations and made sure that everyone felt protected and cared for in some way.
The Martian Manhunter created a well-tuned team to combat villainy because he realised the inhabitants of Earth would require a team to protect them from the horrors of the outside world. With the aid of his friend L'Ron, he was able to put up a team that worked flawlessly and repeatedly save the planet.