While Zed isn't designed to be a late game champion
right now he is one of the best champion in team fighting in late game for some reason
But that isn't really easy to do , needs good timing and the most important thing is to never engage as Zed in team fights , let your front line engage , put a sneaky shadow , at best is to use like triple e and q in fights and try to hit as much as targets possible
Zed has a good late game , if you meet a squishy mage , you can just E AA E AA to kill them , it will take only 2 seconds " which is e cd " you can kill them in in a shorter time than that if you can hit a Q
Your Ult cd is really short so you can actually spam it
Just play around objectives , hide in a bush that isn't warded " you know Duskblade passive " and do your job