Now see, here is the so-called counter bias. As a main, it does not make my word any less relevant. If anything, I understand Zed's counterplay more than most because I have to deal with it and face it. Therefore, I'd say I understand more about his pros and cons than people who simply have to fight him here and there.
There is no point in defending him on these forums. Riot doesn't even consider forum posts when it comes to balance, since most on the forums are low ELO and don't understand balance as it is meant to be. So I've got no reason to defend my main because it won't affect whether he gets nerfed or buffed. Now, by no means am I high ELO, simply Gold 4 but I do know what I have trouble with and what I excel at when playing Zed.
So, zhonyas is your clear cut winner item. Once you get it, you being assassinated by Zed is very difficult. Of course it has a high price. But, you do have armguard that gives a lot of armor and a decent amount of AP. It's essentially the equivalent of hex drinker, although hex drinker is more gold efficient with it's passive up, but worse when the passive is on cooldown. Simply rush an armguard and boots, and provided you don't go spread eagle for Zed's Q's, you shouldn't suffer too much damage. The issue with mages is that they think they are unplayable if they don't rush a mana regen item, so people will rush out a Morello's and wonder why they can't have 20% CDR, 80 AP, grievous wounds, Mana regen to spam spells AND be tanky.
Either rush the whole Zhonya's if your farm is amazing or just an armguard and play intelligently. Watch the shadow. Shadow is on cooldown, lane is yours. Take exhaust, kill potential is yours. Of course, doing all this doesn't guarantee you a win. It's all skill. But, when you have 200 health, recall. Don't sit under your turret because he will ult you and he will win. Just outplay him. And remember he excels in single target assassination, he has a kit designed around that.