Indeed, my bad. The argument still holds though. Overall team disparity should be much higher at low level than high level. A team composed of "Michael Jordan

Indeed, my bad. The argument still holds though. Overall team disparity should be much higher at low level than high level. A team composed of "Michael Jordan + random players" would crush any amateur league with 100% win rate. The same team with "Michael Jordan + Magic Johnson + random players" would probably get 75% win rate in an NBA match. So the metric "win rate" alone, or any other metric non independent of the opposing teams level, is naturally useless in this study.