Interestingly enough, I believe its a common trend to see these "Powerful" champs to have skewed win rates. Because its the "hard to master" aspect that skews their win rates...
I believe Riot is more interested in seeing a champion played to their fullest potential when making balance decisions because: "That is when the system itself gets put to the test when a champ is played to their fullest ability."
So you'll typically see champs like these only really overbearing or in need of tweaks based upon what they are like at the highest skill level... but since these champions are hard to play, many people will try and do sub par with them, affecting their win rates