Ekko isn't broken.
But he does way too much. His kit is practically the definition of 'overloaded', why is his passive arguably better then Vayne's W that she had to give up a skill slot for? Why does his W have such a large stun, as well as a large shield and slow? Why is his E a dash, blink, and and on hit bonus? Why does his ultimate have a base heal attached to it as well as a % of damage taken, with a huge aoe nuke that does 1.3 of his ap?
I get it Riot, you want to make cool and interesting champions, but when it's only fun for the person playing Ekko and just obnoxious for everyone else, I think you just achieved the opposite of your initial goal.