Let's talk about Zed
I want to talk about Zed. I want to discuss my thoughts about him and his overall balance. I think that Zed is strong. However, I would not call him overpowered. I actually think he is balanced fairly well overall. I have played against Zed countless times, and I truly feel that he is not overpowered.
Zed has lots of counters, probably some of the harder counters in the game. From bad matchups to items to negate his ultimate, Zed has so many counters that can make him nearly useless. QSS is a cheap item for carries and it pretty much guarantees that Zed can't kill you in fights, given that he isn't too far ahead. Zhonya's Hourglass is much more expensive, but it always a really good item against Zed, since Seeker's Armguard is a really good laning tool, and it even allows you to start more defensive with a cloth armor and 5 potions since the build path is so good too. Zhonya's hourglass also gives 120 ability power and 50 armor, so it's not really a loss in damage at all, and it makes Zed's ability to assassinate you extremely difficult.
Zed has fair energy costs for his cooldowns. Yes, Zed has some of the lowest energy costs. He also has the least reliable refund and extremely low cooldowns. If you just spam your abilities off cooldown, you'll run out just as fast as any other energy champion. It only takes his full combo plus one other ability before he runs out. His Living Shadow also has a very long cooldown, and he needs this ability to trade well with most laners and he is vulnerable while this ability is on cooldown.
Zed's safety comes at a price. I can agree that Zed is quite safe. He has a lot of range, but at the same time his entire kit would have to be changed to remove this. Again, his shadow has a high cooldown, and he's fairly easy to zone when he is forced to farm with his shadow. He can't harass well when he's sitting back and trying to farm defensively, since his Razor Shuriken's damage is low when it hits another target first.
Zed has poor teamfight potential. I'm not gonna pretend Zed is bad at teamfighting. He can definitely be good in some scenarios, especially during the mid-game where most carries haven't bought QSS yet. However, in the late game, Zed can't always reliably do his job of assassinating. He's too easy too peel off and since most of his power budget is in his ultimate, if it's completely negated, his power in a fight is fairly low.
Zed's ability to escape with his ultimate shadow is normal for an assassin. Most assassins have ways of getting in and out of fights. It's fairly telegraphed, you always know where he's going to end up. It's also predictable, since you can usually tell when Zed will swap back.
Conclusion I think Zed is balanced. He has strengths, but he also has huge weaknesses and a lot of counter play. Thanks for reading, and if you disagree with me, tell me why.