While yes, he was buffed, his R passive was also removed. This means that just because your ADC made a misplay does NOT mean that Zed will now have 30 bonus AD.
You can now clearly see how much damage he's doing. If you're playing a mage just build Seeker's Armguard first then build Lost Chapter. You can shut down his "get ahead" mechanic easily, so Riot is now changing that where he's more reliable in general.