What IS Zeds weakness?

The ban phase.

How to render his ult completely useless:

and

Armor, QSS, death, ban, uhhhh team fights?

he dies when his hp reaches 0

He doesn't have a ranged autoattack.

And with that, I expect Riot to give him one next patch, just to make sure he gets even healthier of an assassin.

flash

His weakness is his ult is easy to itemize against. That's.... it. Not much really when you consider all his strengths. His only weak spot only really matters later on in the game when you're an item or two in, even... and not every champ will be able to rush one of his counter items... so he essentially forces you to counter him or he'll have an easy time doing his thing. He's a bit bonkers right now.