I'm starting to see a pattern here. Why are players who are rank above others are always the worst?

This is the pattern I see in ranked games. If there is a player who has a border indicating they are in a league above everyone else in the team, they end up doing the worst by far. Even worst, it always comes down to them bitching about how they would have done far better had they been playing in a team full of other players in their level.

The hell is that supposed to mean and why do these situations exist? It's come to a point where I loathe to have an incredibly high level player in my team now.