No champion should have over 52% winrate, here is why:
If you really think about it one champ only has a 10% influence on the game because he is 1/10 of the game. So if they have a 52%+ winrate it actually means he would be about 60%+ winrate if you take it as 1v1 which makes the other champs have 40% winrate on average.
Think about how op that is! Mathematically speaking no champ should have over 52% winrate, ever if you want to keep this game balanced.
and
with low stacks and items are less able to influence outcomes then several of stronger early game champions yet Late game they out scale many of those same champions and provide a much higher influence on the outcome.