I've only seen a few times, but my general experiences are:
1. If I'm playing him, I can get kills, but if other lanes feed 10-20 kills before laning phase ends, it's hard for me to help them. This may just mean I'm bad at roaming, or that those games had bad luck.
2. If someone else is playing him on my team, they get kills, but they play with the Riven / Master Yi / Vayne style of chasing kills only, having a bad attitude, and ignoring all towers and dragons (ignoring split pushing Master Yi's). I'm not sure I've won a single game with an Ekko mid on my team other than myself, and I've lost most of the games where -I- play him.
Overall I think his win rates being under 50% at every level above gold, last time I checked, suggests he's not truly as overpowered as some would suggest. This may be especially true once people learn the W range and cooldown.
His numbers are high so he can indeed be annoying if a team chases through his ghost, or if he lands a full combo on top of an unprotected enemy.
My personal suspicion is that he will continue to be banned in something like 95% of my silver games, and that will only change if Riot nerfs something about him. Even if Riot nerfs something by 5 damage, making an almost meaningless change, that might be enough for the general attitude to turn around and stop banning him as much. I'm not sure.
I really don't think win rate is the end all be all for champ power, especially on a champ that hasn't even been out for a whole patch yet.