has been a popular item amongst good Ekko players for a loooooong time. That being said, it was deifnitely not the most popular build (that being protobelt/gunblade builds).
Since preason, Ekko has lost:
The ability to q a wave twice at level one to clear backline
Attack speed (Ekko players know this is important)
This has lead to a much weaker early game, something Ekko has never been great at (Zed can poke, Talon level 2 all in, etc...). In return, with all the damage tackled on to runes, Ekko can actually oneshot people now like an actual assassin. Beating Ekko can be tricky, but given his ~50% winrate according to champion.gg, its far from impossible. The best thing you can do is take advantage of his poor laning. Avoid getting hit by q, which will probably be spent farming the wave, and call for ganks. If Ekko is going FQC, he is spending gold on a support item. Yes, it's strong when stacked, but until then, its doesn't offer great stats. As with any assassin, vision does great, especially since he isn't buying duskblade
tl;dr Yes, Ekko is annoying, but then again, most champs are. Take advantage of his now awful laning, and just like in any game, ward up. He's got a 50% winrate, beating him is possible I promise