Aladar was good as a stand-in leader and provided new ideas to a group in which the current leader was too rigid. Fine, but most of his merit came from his different viewpoints and inspiration of new ideas. After the migration, he just kinda stopped leading.

Simba came back to reclaim the throne and singlehandedly stopped tyrannical rule of Scar. The sequels showed he still is the leader of all that light touches, and still rules well. So basically Aladar times 4.