I would ask you to just wait a bit. A week, maybe two - just to see if his winrate is super high. Now, IMO he is a little op (I would say decrease his passive ration to .5 and reduce the slow on enemy champions), but the thing is, if everyone demands a nerf then riot will nerf him to the ground. He seems like a really fun champion with a lot of counterplay aspects - i would just ask you to hold your judgement for a bit EDIT: Why the downvotes?
Just so you know whiners have been asking nerfs for plenty champs (Zed, LB, Assassin - Tank junglers etc.) yet Riot don't listen to them which I'm glad about it. Forum is full of nerf plz, remove diz champ plz, diz champ veri broken remove it plz threads which shows that how much cancer this community is. Plebs think they know better than the balance team. Ekko isn't OP, broken as delusional kiddos think. Not to mention the assassin hate is real in this community. Yeah Riot eventually tweak his numbers but they won't nerf him to the ground or change his kit just because cry babies ask for it.
Lb has like 43% win rate but she has upcoming nerfs
Actually, his win-rate is considerably low. ≤47% Not surprising considering his [W] is highly televised and his ult makes tracking him significantly easier.
The main problem is in his safety while kiting, because he can ult back and put the hurt on anyone stupid enough to chase him, and his just plain off numbers. Once they tune those back, they can actually meaningfully fix his kit for the better.
I just feel his Ultimate's damage really needs to be nerfed. Yes his ult will be hard to land and you could argue that it's your own fault if you get hit by it...but honestly...For it being a strong "get out of jail free card" of saving you, and healing you and then also deals 500 base + 130% AP ratio as an aoe skill is insane.
Veigar's ult was nerfed for being to strong and his was just a single target skill. Ekko's ult really doesn't even really need to do damage imo, the fact that his ult is a great escape/set-up and heals him should be enough as it is but adding insane damage on top of it is just overkill.
http://champion.gg/champion/Ekko
Plat+ players with more than 5 games on him are winning 60% of the time. This with him being the third most played champion in mid lane. I don't think we're going to be waiting to see if it's super high, I think we're waiting to see if it will drop.
I think it's more likely than not that nerfs will be needed. Considering that it takes 2 weeks for a patch, I expect some preliminary nerfs for 5.11, and then some evaluation from there on how balanced he is.
Sorry, if people have the rights to acknowledge a certain champion who has loads of weak points & deserves buffing, aka 
, then we should be doing the same for 
by acknowledging his strong point which needs nerfing.
Win rate is not a solid factor for balance. Hell, the combined factors of win rate and pick/ban rate are, at best, useful guidelines for how balanced a champion may be. This is because they can also gauge how well a champion is doing in the current meta.
And, honestly, playing both as and against Ekko, I think his numbers are a bit ludicrous.
I am NOT saying he is not op, believe that he is overtuned. I just would like people to wait and see for a bit, that's all
