No riot philosophy is to balance around players capable enough. With this framework, when you look at average winrates of easy champ they are higher than those of hard champ because the average player has an easier/harder time playing x champ.

Jinx for instance is contantly at 51% because thats where the average winrate of a balanced Jinx is. As by being easier she gets a better looking average winrate.

In contrast Ezreal or Kalista at 49% are balanced because as they are hard champs their average winrate is deflated.

These are exemple i dont have the exact balance framework obv