Getting really fed up with these champions

Runic echoes was really meant for those ap champions in the jg who need that burst. So why is it rewarding kind of champions. They can just build it, then build the rest of their tanky indestructible build and then boom free win. And dont say "Oh well they are sacrificing hp/armor for damage" because they arent. You wanna kite a zac? If nobody else is chasing you then sure, but ffs kiting a zac is a lot of work. Especially when you know when hit and you lose 600 health