Thanks to Zilean's K/D/A and utility, he has a fairly average overall win rate. He does very well in the mid game, with a winrate of 50.75% in that phase. Unfortunately, he does terribly in the late game, where Zilean's win rate is 48.7%., The difference between his best and worst game phases is only 2.0%. This small difference shows us that his relative power is flat during a whole round.
Zilean has been picked only occasionally in the latest ranked League of Legends games. In the current meta, his popularity is 2.5%. He is rarely banned during champion select. Obviously, very few players see him as a huge threat. In the latest ranked games, Zilean was banned 0.8% of the time.
You will find him most often played in the support position. The best win rate position for Zilean is support (50,5%). At this time, Zilean's meta game is focused on dealing damage. In particular, his gameplay should mainly be centered around magical damage. Moreover, he is a pretty good tank champ. Dealing physical damage is the least important part of Zilean’s gameplay.
You should expect to have to to dedicate a decent amount of time practicing and learning to get good with Zilean. Many League of Legends players think he is an average difficulty champion to get good at. Zilean mostly does magic damage (86% of his total damage). He doesn't deal a lot of other damage types and should not be played as hybrid damage dealer..
Zilean deals only a little damage over the course of a regular ranked game (10.154 damage). You shouldn't focus on developing him as a powerful champion to crush your opponents. Rather, you should dedicate yourself to assisting your allies to win.
If you are looking for a dominating carry, then you should definitely not consider this champion. He has one of the lowest kill counts in the game amongst other champions. Moreover, he has a fairly typical death rate with an average of 4.9 deaths per League of Legends round. Moreover, Zilean has a high KDA ratio (3.0) with 12.3 assists.