Ekko's kit just has too much stuff in it, and those things, whether they are slows, stuns, damage, speed boosts, or mobility, are all too strong when added together.
He needs some of the extra pieces just straight up removed. No "compensation buffs" either. You don't get those when you're too strong and are getting nerfed.
Like, why does EVERY part of his kit give him damage, but also something on top of that damage?
His passive give him damage (a lot of it) AND movespeed. Also deals double its damage (to a cap, granted) against neutral monsters.
His Q gives him damage twice in a line AoE, can apply 2 stacks of his 3 stack passive, AND has a slow on the first part of the ability, which is the harder part to dodge.
His W, while having a delayed active effect I will grant you, gives him a MASSIVE shield, as well as a large slow field that has the potential to be a large AoE stun instead. ALSO, this ability, which already provides him with survivability and two different forms of CC, passively gives him execute damage on his basic attacks, and because of how he E and his passive work, he is already incentivized to basic attack often as is.
His E gives him a short dash (short, but can still go over more than a couple walls), and then a "I'm coming with you" blink effect much like WW's Q, in addition to being an autoattack reset (remember his autos deal execute damage) and adding a chunk of damage to the blinking attack.
His R is an escape tool that also heals him for a massive amount of damage, as well as making him untargetable (can dodge what would otherwise be fatal damage, like a Veigar ult for example) AND dealing a huge amount of AoE damage.
Looking at all of that, I personally think the first thing that should get nerfed is his overloaded W. Specifically, why does his W, which is already its own ability, ALSO give Ekko Zed's passive, but better because it doesn't have a cooldown on each individual target? Yes, sure, Zed's version can proc on target's who are at 50% HP or lower, but it has a 10 second cooldown per target. Ekko's has no such cooldown, and also scales with Ekko's AP, meaning it can deal much more damage than Zed's pretty quickly. I think the passive part of Ekko's W, the on-hit execute damage, should just be straight up removed. Its unnecessary extra power on an already strong ability. Even removing it, his kit will still have tons of other tools and damage, and he'll still be quite strong.
Alternatively, if they specifically want to nerf JUNGLE Ekko, how about changing his Passive, which deals double damage against neutral monsters? Yes, it caps at 600 against them anyway. Not the point. This will slow his early clear, which is really important for junglers, and will thus have the direct effect of nerfing him specifically in the jungle role, but wont really impact him as, say, a mid laner in any meaningful way.
tl;dr: remove the passive on Ekko's W. Its literally just a better version of Zed's passive, but his W already does enough as is. Or remove the double damage to neutral monsters from his passive to specifically nerf his jungling, his laning will be untouched by this.