Ekko: 1.2 AP Ratios

Ekko's reliable damage(first hit of Q, bonus magic damage of E, activating his passive) has a 1.2 AP ratio. Fizz(a similar champion in some regards), has 1.95 AP ratio with just his Q, E, and one W-empowered auto, ignoring his very short delay ult.

The rest of what Ekko can do(incoming timewinder, ult, 2.25 second slow) has a 1.9 AP ratio and a shield + stun, sure. It also has at least a THREE SECOND DELAY. And for two of those abilities(timewinder, ult) you can see where he casts it.

If you're low enough health for Ekko to oneshot you without counterplay, any other mage or assassin could sneeze in your general direction and you'd die. And likely do so from far greater range, as well. He just requires players to actually think about what their opponent is doing instead of dodging on reflex.