Maybe if Ekko had less things in his kit and was easier to play, he could be made more balanced... I wonder...
I feel Ekko's issue is less about "kit has lots of things and is sort of complex" and much more "Ekko's kit has amazing tools for a tank and mediocre tools for an assassin"
Self-healing, HP shields, AoE stuns, jumping into the middle of an enemy team for AoE damage, and short dash to get you there: sounds a lot like Shen, Sejuani, Zac, or Nautilus.
Ekko is much more a tank with the aesthetic of an assassin than he is an assassin that's abusing tank items.
As Ekko's short-range dash is pretty much the only thing that supports a melee assassin play style (where you build pure-damage and survive via speed, or "never stop moving"), he's got the same incentive to build glass-cannon DPS as tanks like Shen, Sejuani, Zac, and Nautilus.
I wouldn't expect AP damage builds on those tanks to do well either.