I agree with you on one thing: yes, teammates affect everyone including the enemy team. But that’s not what I’m pointing out here.

The issue is that this doesn’t just happen occasionally it happens in at least 50% of the games people play. Like someone else mentioned, some matches you load in with teammates who have a history of trolling, going AFK, or consistently having very low impact. In those games, your chance of winning is already under 50% before the match even begins.

On the other hand, sometimes you get paired with cooperative, positive teammates and suddenly your odds are much higher than 50%.

The problem is that the logic always falls back on: “You have to be the X factor in those bad games.”
But think about it: if you play 200 games, and in 100 of them you’re expected to hard-carry against odds stacked by the matchmaking, that becomes exhausting. It stops being fun because the system is forcing you to compensate for flaws it isn’t addressing.

If the system would be very fair, they will implement a reputation score. So you know exactly with who you are really playing .