You're basically ignoring the show's entire content. It had substance, stop being prejudiced and try to watch it with an open mind. Gurren-Lagann is a "memento mori" take on the concept of progress. The quirks of the classic "coming of age" tale such as honoring your legacy, change, breaking traditions, reciprocal individuality or burden of responsibility were only used as a way to bring this idea to a more personal level.
The show states from the first episode everything they want to accomplish with their storytelling. And they do it naturally, without clumsiness and resourcing to only dialogs and characterizations. The basic ideas that drive the entire plot and everything comes across fairly strongly from before we even know what a "beastman" is.
From a history of failure, Jeeha village came to the belief that no future was possible for them in the surface. Imagine the Middle Ages and their belief of a flat world. The way the dialogs deliver this idea is pretty neat. Characterization is delivered on two levels: the character and the idea behind the character. The village elder forbids Kamina from trying to break through the surface, but only because it is "his responsibility as leader of the village". Kamina's rebellion is not in defiance to authority, but him trying to fulfill a promise with his father. All of these ideas become the core to the narrative as it progresses. Doing the impossible was not so much doing the impossible as it was doing what was believed DUE TO FAILURE to be impossible. Progress was not so much a trying to destroy tradition but rather tying together the past with the future. Oppression was not so much the desire for power but rather a responsibility from those in power, from those that came before.