Zilean is the perfect counter to melee champion especially with the crippling E
Have you ever tried to get close to an adc with Zilean pressing E on you and crippling your movement speed to 112 for exemple. And feels aweful getting outplayed by a ranged point and click that is up as soon as it goes on cooldown? I played morde that match and felt aweful not being able to do anything during a teamfight being crippled down.
's W is basically the same... But with a attack speed slow on top of it and lasts longer.
is suppose to protect his teammates, even from assassins. That is what he is made for.