Why does Zed bring so much more to the table than other assassins?

I just lost a game to a damn strong team comp. And I'll admit my defeat, but how come zed is able to sacrifice an item slot with randuins become semi tanky and still out-damage a full pen damage built Talon because of his passive % damage increase?

I just can't understand why he has so much freebies with his kit, I'm convinced that if he had his extra damage steroid removed he would be 100% balanced. But as it stands with the rest of his kit it's just overloaded with things that keep him ahead even when he's behind. I mean if you're going to have a nigh resourceless assassin with long range poke, un-punishable ult if he messes up and add free damage ontop of an already amazing passive that allows him to almost never miss cs. There has to be a downside to his kit, I honestly try to look at it critically and see if I can find weaknesses but I just can't find enough to justify him being the way he is. I mean sure you can build a zhonyas and say it counters his ult, but his damage is so damn high he really doesn't need it to delete someone.

I'm not saying he's completely op, but he definitely has an overloaded kit. I believe the power should be shifted into allowing more counterplay instead of having to sit at your turret all damn game trying to play dodge the resourceless zed poke.

Honestly I find it disheartening that my favorite assassin is completely overshadowed(Ha!) by almost every other assassin except If you can really even call her an assassin. But with the current way things are it's just disappointing to see Zed every other game and expect the same outcome everytime.