Zed is not a healthy champion.
If your standard is being less toxic than Akali, or most assassins, sure. That is setting the bar pretty low. Relative to most champions, no. I'll try to be concise and go over why I feel Zed is unhealthy. I feel that Zed has such a complete set of strategic and tactical advantages that he's not healthy.
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Laning: Well the fact that he can get his CS consistently under any form of pressure aside from being killed. However, he is among the best at escaping from ganks and bad situations. Safe laning like this is not necessarily a problem by itself. It is a problem on a champion who can engage, burst, and disengage so fluidly and safely. Most champions who are so dangerous can be shut down early game which reduces their threat mid/late.
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Engage: Zed can engage from a huge total distance between W and R. This is a low counterplay engage due to the distance he can engage from. To make it worse, he can dodge all enemy engages with his R while engaging himself.
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Disengage/Safety: Zed can instantly disengage after he uses R, and he can choose to do this after he has done his whole burst combo. After such a powerful and versatile engage he also has probably the best disengage? I'm not sure how this is supposed to be a healthy pattern at all. I mean, he can even R, then R instantly before doing anything... and it leaves a shadow next to his target so he can still hit them with his skills. Given another moment he could have left a W shadow there too to get more damage.
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Lack of counterplay: The idea that Zed has a lot of counterplay is a big misconception because most of the ways you can stop him are with long cooldowns which are hard counters to his kit. However, stopping him from getting a kill when he engages doesn't put you at an advantage. It just forces him to disengage, which he can easily do. He doesn't have to commit. He can easily force you to use important cooldowns just by ulting you and he doesn't put himself in danger by doing so.
So what I'm trying to get to is, how are you supposed to do anything about Zed? Yes, it's nice that you get a lot of warnings about what he is doing. The problem is you can't do anything about it. You can blow cooldowns or die.
he is strong in almost every position he is in when played right and doesn't have any many weaknesses besides late game when everyone has had a chance to progress their builds farther. He could use some toning down, not some heavy nerfs like they did with Elise.