Everyone was so distracted by tank Ekko
...that everyone forgot how broken and overloaded AP Ekko is, too.
He's frustrating to play against, forces you to burn all your important cooldowns and presses R, so he negates all your damage and can go in again before you can fight back, or you save them and try to kite (LOL) and get AAed to death by his passive and insane stickiness.
He is easily able to farm the whole wave with Qs withou running out of mana (people are going to try to convince you otherwise) and if anything goes bad, BOOM, R safe button. Impossible to punish.
Is that enough? No, because his E just needs to proc on hit on top of it being a low CD dash + blink, the way he doesn't loose a pushing power.
I say, give his ult at least a half second cast time before the invulnerability triggers so we can interrupt it with CC or just remove the on-hit part of his E, it's so damn frustrating to be oneshot by a targeted double-mobility spell.