If Zed is becoming a problem in the next days...

Instead of nerfing his damage, nerf his Magic Resist per level. Instead of him gaining MR, let him stay at 30 MR and no MR per level.

What is the reason that Zed gets free MR per level, and not Yasuo?

Yasuo, if I recall correctly, recieved no MR p/ level due to him being an Assassin in the mid lane and having a close range fight against most AP mid laners. Zed, on the other hand, get's free poke from his range and thunderlords. Zed also get's Maw of Malmortious if he is having a problem against his opponent. He negates everything from a burst from his opponent.

So, once again, don't nerf his damage. Nerf his MR and MR per level. Once simple nerf that surely will make him less annoying to deal with.