Ekko's Shield, Stun, Slow, Passive extra damage, whatever you want to call it is a very huge part of his kit, it's his most overloaded spell. I honestly wouldn't mind Ekko if they just nerfed that w passive, It literally makes him such a good farmer and gives him such a strong early it's ridiculous. It's like a little bit worse version of Zed's actual passive.
And if the stun and slow went something like this
1.5/1.75/2/2.25/2.5 (which max level it is a longer stun than it is now)
and slow decreased over 2 seconds from 40%
Honestly Ekko would still be great, but it would remove the power to have an extremely stupid fucking strong lane bullying phase, but still increase his late game potential on the stun landing.
Edit: Ekko is point and click insta popping, strong engage power. I honestly don't know what you're saying here, or what your argument is. Since a lot of his damage comes from Ult and basic attacks. Ekko's Ult punishes any chasers preventing any kills when he escapes.
However I do agree on the nerfs Riot did to Kassadin and LB, not the newest pointless ones that made Kassadin tier 4, but when they removed that god awful silence. I'm just saying they're kind of pulling a Kassadin. They remove most of Kassadin's mobility, and his silence, but they they give Ekko insane engage power, and CC in one ability.