How do you explain these ARAM winrate oddities?
https://lolalytics.com/aram/worldwide/platinum/plus/champions/
Why are Sion and Maokai in the top tier winrates?
Maokai I can kind of understand if his ultimate is the basis for winning teamfights, but the rest of his kit doesn't seem useful when ultimate is on cooldown. Seems like too much of his value is tied up in his ultimate for him to win so consistently. Unless it's really just that powerful and braindead to execute. It covers the whole bridge and goes so far that you'll either root the entire enemy team to be pounced on or force them to retreat entirely from the turret. But if your team can't follow up, or you use it at a bad time, you're just a potato sitting around in lane for 2 minutes while you wait to try again.
Sion, I'm having more trouble figuring out. Is it just that his passive is that powerful in a 5vs5 clustered ARAM environment? You might be getting rewarded for suiciding into the enemy team with your ultimate and then pounding out a kill or two after death. I don't think his ultimate by itself is particularly powerful in this environment. He's probably helped by the fact that his Q is a stupidly long range and easy to hit poke, unlike most juggernauts - but I don't think that alone is going to carry him through ARAM.
I'm also surprised that Xerath's winrate is not higher. I personally would prefer getting Xerath over Ziggs in ARAM. Xerath has the highest pick rate though. So obviously people think he is the best for this, but either they overestimate his value or people just aren't good at mechanically executing on him. Maybe a ziggs is easier to hit stuff with.