http://matchhistory.na.leagueoflegends.com/en/#match-history/NA1/48895943
This is how well a good EZ can do with him lol, look at it.. even in his lost he still had a good KDA lol
He does a lot of damage over time cause of his passive attack speed steroid plus you cant never catch him as well so hes doing constant damage to you and you cant even land one lol thats the problem. But then again I dont think hes too op, just really strong.
Hes basically a monster if he gets ahead cause then he will actually do alot of damage, if he doesnt get ahead he can wait and scale up and be strong late game cause he can always do constant damage without getting caught. Hes good at all phases of the game and thats not something a champion should have, every champion has a fall out somewhere but thats not the case for Ezreal. And thats why he has such a high win ratio, if you cant kill the ADC you cant win the game most of the time.