I can't really agree with the "Safest Champ" part, his W has a ridiculously long CD and is the key to his trading without using his ult. I don't think his damage is too insane unless he snowballs either, which is the case with a lot of Assassins.
The thing with Zed is that he isn't really a strong early game champion, people just call him safe because he actually has an escape (Like other viable assassins these days like Leblanc). He is more Mid-Game focused where he looks to pick on immobile carries and Split-push if he can. His damage is relatively High, but then again he's a midlaner, where the majority of champions who go Mid can 100-0 you if you are out of position (It's kind of their job to do damage) and I can name a few champions who are just as safe as Zed is. He has poke damage, but he has to sacrifice his escape to use it effectively.