Ekko is one of those champs that isn't the easiest to properly pull off, hence why is so close to the botton on most lists because they don't account for "extensive practice with him", but a "pick up and play" with a potential of "decent amount of practice" (aka, 10-20 games) for the things. I mean, some lists even set the "mechanically intense" champs at a 30-40 game "learning spot".
Ekko isn't hard to learn, but he is hard to master, and just being decent at him isn't as rewarding as being decent at Zed.
LS said in his latest patch rundown that there's the Korean challenger called the Ekko God who almost always has a 60-80% win rate on Ekko in Korean challenger, and the Ekko, if you're able to properly pull him off, is stupidly strong, but similar to Taliyah and other champs, not many can, so he's at the bottom of the barrel because of those people.