win rate by games played (theory)

Every once and a while I will see some data that says that players on a champion with 125+ games have smaller win rate than players on that champion with 50-75 games, say. Always wondered why but now I have a reason:

They climbed. Players who played that champion 50-75 games climbed high enough during those 50-75 games that they had a much lower win rate during their next 50 games. And that made their win rate average go down because tougher elo.