The issue with Zed is his extreme safe poking in lane against mages who SHOULD poke better than him but, sadly, cannot get to him. He is safe for having to melee creeps to kill them, even though he doesn't have to (Shuriken, Living Shadow). Yes you can avoid his Shuriken and Living Shadow, but often this means you have to miss out on creeps and experience, which also leads to the point that he can zone better than most zoning mid laners. Now in the best case scenario you avoid his Q and his W and you can farm, but this is pre-6, post-6 if his living shadow is on the field even if you are full health you might as well stand far back and wait for it to go away, as he can still all in you for the easy kill. That is the issue with Zed. Most mages in the mid lane require either poke or all-in, but if a mage has to all in, they do not necessarily have a safety feature built in like Zed does. Yes there is
who technically have "safety measures" but not to the extent of safety Zed has. If Ahri messes up she is either dead, oom, or hiding under tower for a bit. If LeBlanc messes up then, well, she didn't get the kill and is probably out of mana or in a bad spot. Akali is Akali she has twilight shroud but that is not always going to help her. Zed, if he messes up he can go back to his far away shadow free from harm and he can try again later with the same safety and no retaliation fears.