This tank Ekko thing
It's time to bury it. Ekko is supposed to be played as a skirmisher, almost the ultimate mix of cunning, mechanical skill, and intuition. Tank Ekko removes that necessity entirely. As an AP Ekko player since his release (I have never ONCE gone tank), the fact that this play style works is insulting. Ekko is a great champion, with possibly the highest counterplay among assassins.
With that out of the way, here's my suggestion: Nerf the bases of some abilities, and change all the slows in his kit to scale out of AP. If necessary make the stun 1 second rank one and current duration at max rank.
It saddens me that it's come to this, but frankly it's better than continuing to be insulted by this disgusting display.
Edit: At the timing of this edit, he is/was being played Mid Tank in the LCK.