I have proved two criteria that require a ban:
1. character somehow breaks smash game play
2. character is unbeatable
only 1 of the 2 being required. Metaknight can be beaten, so that nullifies #2. Metaknight does not disable the key aspects that encompass smash game play, such as free movement, the ability to attack, defend, DI, or outplay your opponent, so he fits neither criteria.
While I'm at it, criterion #1 was the reason I wanted Wobbling banned, as it effectively DOES break smash game play.
smash game play does not encompass countering, as countering is not an element of smash game play, but rather countering is an element of our tournament format. the lack of counters does not leave MK to break smash game play, although I do believe him to have no counters.
edit: akuma breaks game play in his game, removing the ability to attack, thus warranting a ban. akuma actually fits both criteria.