From what I watched, I believe he was acting reasonably in self-defense. I would also point out that each individual attacking or chasing Rittenhouse should be looked in the context of being part of a mob. If a mob is coming after someone, there's no proportionally reasonable response to each individual. If any of them die that's on them.
Similarly - if a mob attacks attacks someone driving, hit the gas and run everyone over. It doesn't matter if the driver kills someone who is just standing in front of the car and not the one swinging a bat.