I think the issue is that, outside of formal tournaments, there are rarely stable teams competing against each other in typical online multiplayer. each team is

I think the issue is that, outside of formal tournaments, there are rarely stable teams competing against each other in typical online multiplayer. each team is a random assortment of players, where anywhere from zero to a full team are queuing together. people might queue with a friend of a very different skill level. you need to track the skill level of each individual player and then estimate the win probability for a team of players who may never have played with each other before. I play a lot of csgo, and while far from perfect, I'm surprised how good the matchmaking is. I win pretty close to 50% of my matches.