Originally Posted by
Ra-El
You are right. Superman, the Unbeatable Champion, became Superman, the guy someone kicks to show how cool they are.
At some point, DC as a whole realized that it was way easier to use Superman to show how powerful, cool or skilled some character was, than doing the actual work to establish it. So when Miller wrote TDKR and needed a great ending to his love letter to Batman, he decided that having him beating Superman was a good way of showing his Bruce's ingenuity and perseverance.