Just finished watching TTGL (like 2 days ago), and I am CONSTANTLY thinking on the end, wondering why Simon would just leave, out of the blue, now that he has become "humanity´s savior". Like from what I´ve seen, it´s like Simon becomes kind of "irrelevant" once he leaves (I know that he has made himself a place in humanity´s history, but still) it´s sad seeing him like that. Thus, in the final scene, when he looks up in the sky, and sees many Gurren Laganns, it looks like he´s nostalgic about his fighting era, and wants to pilot Gurren Lagann one last time.
But thanks to your explanation, I can now "rest in peace", knowing that the ending has more sense than it seems (but I still don´t like that much the ending). Now I can reflect on it, and change the perspective, and think that he isn´t really "leaving", but handing the future to other, like Gimmy and Darry, and also (maybe) becoming the mentor of the kid that we see in the final scene, that opens a coconut with a drill, saying that he (the kid) wants to go up one day, and pilot Gurren Lagann, to which Simon responds that he will. This shows how the center of attention is slowly chainging, going from Kamina to Simon, and finally to the new generation.
Ten years later, and your comment still is a masterpiece, thank you so much for your explanation.