Dude, even though I have my preferences I don't let them supersede the way I look at the story as a whole. You are. I wanted Zoro to fight Kizaru but that hasn't happened as of yet. You don't see me raging and pulling my hair just because shit didn't go according to what I wanted. This flashback is gonna have a lot of focus in the idea of Nika and what he represents to the opresssed. It makes sense that Luffy would be the first to punch a so called god and actually hurt him in front of Bonney.
You on the other hand are solely concerened with Kizaru's portrayal and him "getting back up guys, he actually won the fight I promise" While I think this fight is over now regardless. From a thematic standpoint, it makes sense for Luffy to fight and defeat Saturn.