Win Rates Don't Matter
Win rate does not matter. A champion is not broken simply because it had a higher win rate than other champions. There are many factors involved in win rate. -Riot
Riot has been wrong so many times. I understand that if a champion has a lower play rate and a high win rate there's a chance that it is just a slight anomaly, but when a champion is in 1/20th of games and wins 57% of them several patches in a row it's no anomaly at all. I'm talking about ivern in the example above. I'm going to explain build paths and win rate. Basically, anyone who builds cinder hulk on ivern will only win 45% of the time, this is because cinderhulk is a bad item on him, you can buy much more cost efficient items.
Ivern's high win rate comes from when you build support items like redemption, athenes, and locket on him. In fact, you win 62% of games with these 3 items. When combined with ardent censor this increases to a WHOPPING 68% WIN RATE. Why?
Cost efficiency and gold income. These items are completely balanced on support champions that have lower gold income. However, ivern has super high gold income as a jungler. He buys these items faster than any other support and then, he becomes better than your support.
Here I am presenting to the 2 different win rate statistics: overall win rate and play style win rate.
Overall win rate- a champions win rate over all games played. Is typically a bad statistic since low play rate could spike it or could be lower since lots of inexperienced players use the champion with the wrong playstyle/build.
Play style win rate- the win rate of a champion when used and built properly.
Example of overall and play style win rate: Last season, sated devourer with guinsoos rageblade was broken on master yi. This combination of items had almost a 60% win rate. However, mosy players actually still built warrior on yi which only had about a 45% win rate. This brought his overall win rate down and made him look balanced.
TLDR; overall win rate doesn't matter, what matters is the win rate of a champion when played properly (with a specific build).
Most statistics from www.lolalytics.com