So I played against Ekko as Ziggs.
And I got destroyed. Like demolished. Granted I was a first time Ziggs, but I don't think that it accounted for all my deaths. Like nothing I did made a difference. Absolutely nothing. I tried hanging back, but he could still engage on my. I literally couldn't AA minions without him going all in on me.
So after the game, I went to the wiki and compared the ranges. Q: Ekko 1075 Ziggs 850-1400 W: Ekko 1600 Ziggs 1000 E: Ekko 750 total Ziggs 900 R: Ekko Global Ziggs 5300
Now I get that different champs are different, but Ziggs is a long range siege mage while Ekko is an assassin. Except since he is longer range than a siege mage, I'd say he is also a siege mage. Okay, maybe Siege mage is the right way to describe him since he doesn't play like that but he still out ranges them.
And he also beats out Xerath. Q: 750-1400 W: 1100 E: 1050 R: 5600
And Vel'koz, who is probably the longest ranged champion overall, barely out ranges him. Q: 1050/1485 W: 1050 E: 850 R: 1550
But not only does Ekko out range these champs, but he also out damages, out ccs, out mobilties, out bursts, out dpss. And this isn't even mentioning his "oh shit" button.
I fail to see any major weakness that Ekko has.