He did get a small love tap, baby nerf a patch or two later but the main nerf that's needed is a Q nerf. A riot defended and gave a reason for not nerfing the Q and instead of the W, but I disagree. He's Q is a lot stronger than Ekko's, and a ton of other mid laners Q's. It's a lot safer to use scott free from any damage.
The item Duskblade in itself is very strong, it can work on Shaco, Rengar, Kha'zix, and overall just a ton of champions. Of course it's tailored for Zed the most, but honestly, Zed is the problem, even when he doesn't get Duskblade.
He has the most outplay potential in the entire game, he's hard to gank when he can shadow his way on out. His ultimate is already bullshit, gonna be more bullshit after the QSS nerf, and really, you gotta trim this power by nerfing the Q. No it will not break him Riot, it will level him out so others don't get their HP bars drained under 30-40% by the time they are level 5.
To be fair, he isn't the top of the ban list at the moment for me, it was for a few weeks there, still my number 2 ban if anything tho.
Also you can't just buy "Zhonya's" against him. It costs way too much, he will have a hexdrinker and upgrade it before you get Zhonya's, and already have some kills on you, So yeah. while Zhonya's is an awesome item especially against a Zed, it takes longer to get, even after the item changes upcoming, it still takes awhile.
Seeker's needs an upgrade. It should have the Zhonya's active effect. Yes that would be OP as shit, but seeing that Hexdrinker prevents them from dying and stuff after you land a ultimate and what not, Seeker's does need something. Maybe prevents lethal AD damage once you are under 40% or whatever like Hexdrinker.