The Saints did it with an elite offense and a defense that played Brett Favre and had 6 turnovers in the championship game. They were definitely middle of the road but had a very good turnover margin. If "elite offense+middle of the road defense wins super bowls" was true the Packers would be 5x Super Bowls straight. Also that Denver offense wasn't mediocre. It was bottom of the league. Also the unicorn of elite on both sides has happened for at least one team every year for a while now. They just don't necessarily advance to the super bowl every year.