Well, ekko does not have the dmg to delete ppl from 100-0 UNLESS
Its sona you are trying to delete AND you got fed while also rushing
If you can get these two items before lvl 10-12 then yea you can basically delete ppl for the whole game, but you wont have time to build cdr if you want to keep that dmg up.
If you want to play ekko with a cdr build, you have to get really good at being disruptive and u need a team that can keep up a little bit and capitalize. U basically try to force ppl out of position by using your q to zone and stuff. Works well when your team has some pressure to add onto yours. Then someone on your team can land an ability and you rinse repeat until eventually the enemy is so disorganized u can go for a full q e combo.
Advice:
Try to learn your passive's cooldown, if you go cdr build. U will probably do better if you can start proccing it more than once on the same target. Q E back off Q E ulti. That kills tanks.
Also, build
.
Also, try to use your speed to "go off screen". Sometimes I have to qe a tank like maokai to get a fight started in my teams favor. My team follows up on that powerful slow from my passive and while they do that I go really far away and then circle back around. The enemy will probably forget about you for a second because they cant see you. That helps them do something stupid like focus a tank. Then, before you know it, your cooldowns are back up and you are ready to w q e the adc. Pretend to be a air to surface fighter plane. U go in and fuck shit up then fly away. Then you come back and do it again when they arent ready.
U can use the fact that you do a lot, but not a whole lot of dmg to your advantage. U dont do enough dmg that they arent willing to fight. U do do enough dmg that u can fuck them up. U just have to do it a couple of times He is a time winder man. Gotta run that shit back and do it all again.
Also, think about who you really want to get fed. Its probably your top laner or jungler. not the adc. So gank the top laner a little.