The Ekko nerfs weren't sufficient. I propose a Better way to nerf Tankko.
The only way to destroy tank Ekko besides from completely redoing the champ, is to punish him for building tanky.
I'm thinking something like: -For every bonus 20 magic resist and armor, he loses 2 MS. Let him be weighed down by the guilt of building tanky. -For every 100 bonus health, he loses 4% of his overall damage.
No need to buff his AP. Just make it that building Tanky would literally hurt his other stats.
and yes, that includes items like

Riot please consider.