Assuming there are no ties, and teams have an even number of players, a multiplayer competitive video game is going to be a zero sum game; for every winner, there is going to be a loser.

While I agree that you it isn't the SOLE purpose of a matchmaking system, I do think a fair matchmaking system will end up with most players having a 50% win rate (with a few people at either ends of the skill spectrum having lower or higher win rates). If you are winning more of your games, you should play better at better players until you start losing again (and vice versa). You should eventually hit an equilibrium where you are playing people you have about a 50% chance of beating.