There's also "Jonathan's body was rejecting Dio, so he clearly wasn't as strong as he was in Part 1. Despite that, he was still able to outspeed Joseph without using The World. Jonathan beat him in Part 1, so he is naturally also faster than Joseph-who has lightspeed reaction times." They both come down to deciding that Young Joseph can react to beams of light, and wasn't just using his subconscious precognition or insane luck to act before the light started to move, and then trying to find a way to scale Jonathan to that.