Cage can definitely win tournaments. It's not like he's completely defenseless in his bad MUs. A good Kenshi or Kabal would be his biggest obstacles at a tournament, but they can definitely be overcome.
Question from a non-MK player, just from what I've gathered watching matches: Does any character in the game have remotely close to the chip output of Cage with standard blockstring pressure? When I see Dizzy play it's like every round he does 50% of the other player's health just off pure chip, it's insane relative to other games I see.