https://www.leagueofgraphs.com/champions/winrates-by-xp
Yasuo goes up to 52% winrate with experience
Even more interesting, and a complete nullification of this argument, is that yone winrate increases a full 10% with 50+ games of experience, up to 58% winrate.
These champions are extremely popular and high skill-ceiling. Bad players love these champs and drag their average winrate down significantly.
Phreak is speaking, as usual, with one of the most shortsighted and self-involved perspectives possible.
You have several huge errors here:
You assume all champions are equally "not-mained" before claiming that the "mained" winrate is the accurate number and so the winrate delta is actually how much skill growth is available. That's a fatal flaw. The last time I had hard data (2017), Yasuo was top 3 for most-mained and had one of the highest winrate growths for experience in the game. So a ~5% winrate lift for Yasuo should tell you a substantial portion of Yasuo players are already mains, which echoes my point.
Unless you manually changed things, you were slicing only plat+ data, which, even a day later, only has 388k games. 388k games divided among 160 champions and then further divided into the subset of players with a lot of experience is not a lot of games. You're going to get massive variance. For reference, I changed Plat+ to Iron+ (i.e. all games captured by the site) and the Yone difference went from ~10% to ~5%, or 64th. I don...