Is John Gruden one of the most over rated head coaches ever?

In Oakland he was fired because he couldn't win that great team Al Davis embled for him. Then he goes to Tampa where he wins the superbowl with Tony Dungy's team. This was followed by two below .500 seasons. He was never able to make it past the wild card round in the playoffs and when he got his team there he got smacked by NFC East teams. Is he really that great of a coach or did he just get lucky once?