IF we really wanted to nerf Zed...
Couldn't we make it so his ult only doubles all physical damage? It'd make Bork a less appealing option to him, since it's 10% max Health Active and it's 8% of current health damage, can do a lot to a healthy target, pushing him more towards Hydra.
To make up for him losing a lot of damage, we could morph his Passive into more of an execute that deals damage from missing health, but lowering the threshold to around 30%-35% health.
I know this would require a bit more polishing and refining in places but hey who knows.