Yeah, winning Olympic gold in Brasil is a real horrible performance...

Little brothers watch older brothers carefully. They spend their entire lives noticing where the older one made mistakes and then try not to make those same mistakes. Being at least a 50% genetic match, they capitalize on these advantages and also are motivated to try to compete with the older one. You end up with an athlete that is often wiser, stronger, faster, and more competitive than his sibling and is just waiting to take advantage of an opportunity when it presents itself. I wouldn't be surprised if Jonathan is the one that eventually races and wins Kona if Alistair tries and fails.