I main Zed and it's tricky, it really is. I'm trying to stay as unbias on this as possible.
Zed is mechanically hard to play/master, and many people debate this. When you play against zed, people don't really appreciate all of the mechanics that go into the play. You will hear people just say "Oh, just hit r,q,e bork, AA,r win" but it isn't that simple. Zed is given such a safe time because there are items that completely counter him. Zhonyas is an example which is staple for AP mids which is who he tends to fight. When zed ults someone and they zhonya, 2.5s of the 3 s deathmark is wasted. Zed is now currently in the middle of everything with an invulnerable target. It would be ridiculous not to have his escape r because then zhonyas would be a no-counterplay item to anyone facing zed. QSS is an item largely ignored by lower elo people largely because it is relatively expensive but it can be a life saver. CC/peel, qss, zhonyas, exhaust, mobility - basically anything to keep zed from utilizing his death mark effectively is all a part of zed's counterplay.
Which brings me to safety. People talk about the shadows as if they're a get out of jail free card. They are not. Anyone that's ever played Zed would know that. I know it is EXTREMELY frustrating to see Zed ult you at tower when you have about 1/4 health left, e, swap shadows and hit you with a q for the kill and take all of one tower shot if that, however I can't tell you how many times I've done that exact play and had fucking xerath or ziggs insta-cc me resulting in both our deaths or just mine. The counter to Zed's shadow play is cc and predictability. You can see where his shadows are. There should be no surprise as to what he does. I've had people cry because I throw out a shadow for an e-q combo, then walk away and they just waltz up to the fucking thing to cs and die because I swapped to it.
It's true you can't stop zed from cs'ing. However, he is like leblanc in that matter. If he's using his spells to cs, he's not using them on you. And contrary to popular belief, zed's ult is not instant death. If zed hits level 6 and you're both still at full health, his ult won't 100-0 you.
Zed has safety, but his safety is extremely predictable and counterable. Zed shadowing away from a gank is the same as katarina shunpo-ing away to a ward placed on the ground. Same as leblanc's extreme juking potential, same as ziggs and his great cc-escapes.
The biggest issue with zed's safety is self inflicted actually. People react far too quickly, as ironic as that is. When zed ults you, he leaves a shadow from his departure point and appears wherever you are (minus teleport and recall). The biggest mistake I see is me ulting someone and before I appear, they flash, they dash, they jump, they something. All they did was burn an escape cd crucial to countering me and made my "Safe escape" all that much better. I think that people would have an easier time vs zed if they worked on their own timing. Zed has incredible mechanics that can allow him to do ridiculous things, however he can easily mess up in those mechanics and that doesn't mean he has to die for it as GD seems to want to believe, it just means he won't accomplish his goal. Remember, zed ulting your carry, fucking up, and r'ing back to safety is a win for you. He lost his ult, and you kept your life. Zed ulting your carry, succeeding, and getting out is him living up to his assassin concept. And as a zed main, I can tell you that peeling and cc works wonders. Something as simple as a draven knockback can ruin the whole thing and enough hard cc results in failure and death.
Oh, and a side note. Zed has remained about the same since his rework last october. The only reason people are crying now so much is because he's the last true assassin that hasn't been hit hard with nerfs. It isn't harder to fight zed now than it was before for any reason. It's just that there's nothing to compare his power to now so people just say nerf him too. Long live Syndra an Xerath!