But you responded!
What's equivalent to what is obviously opinion, but I think many would agree that a game of umvc3 is roughly equivalent to a round of ultra. Do you disagree with this?
In my opinion, time should be the deciding factor. The TO should decide what the average length of a match between two players needs to be (across all games). Then, run each game to fit (roughly) within that parameter. For example, if it's decided that 10 minutes of play is appropriate/practical for judging who the better player is, adapt the number of games/matches for each game individually to roughly meet that goal. That's the best way to do things fairly, no?