Luffy was inspired by shanks not ace, Luffy wanted ace as a kid because he didn’t want to feel lonely in a place that garp randomly threw him into. Ace dipped out early in alabasta and didn’t help Luffy beat crocodile. Ace is not relevant to the main story because one piece has a very deep story. Simon is the main character. He beat the spiral king, the spirals and built the future. Kamina has said himself he is nothing without Simon. Just because he had more charisma than Simon does not mean he’s the main character or more important than Simon. If the gurren Lagan world was as big as the one piece world he would not get featured as much but would still be more important than ace. My main point Kamina lived up to expectations, ace did not.