DegnanNetworking is the most important skill in tf2. Almost all advanced+ teams are circlejerks, and they don't pick up players who are not a part of their clique. I have no doubt that there are players who are better than me who have had less success because they don't have the friends I do, and similarly I know there have been people worse than me on better teams for the same reason. It's just the nature of small, team-based esports. I'm pretty okay at the game, and yet I owe almost all of my progress/success to being in a clique of talented friends.
Ironically, ridiculous DM (independent of gamesense) is the one great equalizer here, because the one surefire way to get around networking is to utterly dominate in pugs. DM donkeys can get headhunted by good teams, while brain players need to make their own and build up a core.