So apparently Yi mid counts for one of Ekko's counters
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1866613863/214360882?tab=overview
By 15 minutes into the game, I've killed Ekko 3 times and destroyed his tower.
Yes you can say their Jungler was AFK, but it was a Yi Jungle and I didn't receive ganks from Zac because I believe he was camping bot, so I can assure most of the fighting was 1v1s and both of us roaming bot once.
Apparently Ekko is squishy as fuck early game, so if you care to dodge his Q and engage on him, it could lead to an easy kill.