You are right Meddler, I think lowering stats just because yes, is not a good idea to deal with the character issues, nonetheless, I have analized and practiced with the new change and I just found myself with a dilema: You talk about reducing his offensive and non punishable killing pattern with Death Mark shadow teleport, but you are also hitting his defensive or "juke" power, have you tried to escape using Death Mark? Now is almost impossible.
You know that 1 second is a LOT of time talking about the gameplay of an assasin.
Another point, you made Zed's Death Mark to create the shadow in the original position as a safe point, a less abussive ultimate, but now you are taking away a part of that factor or "ability" you gave him.
I'm not here to convince you to change what you have done, mostly because sadly, I'm not a designer, but I've played Zed so so so many times that I 've lost the count.
The moment I play against someone who knows how really Zed works is when I feel the nerf so hard thus is not a good experience for me to know that if I try to kill someone bursty like me I will also die, in a normal situation I won´t kill my target in 1 second even throwing my whole combo in 0.5 seconds, I'll have to wait for the mark to pop in order to assassinate, if that target is not a burster it will be a ccer and we have the same uncomfortable situation where I cannot even rely too much on the W because it has a lower range than the ultimate and it is slow and doesn´t make you untargetable...
In this case, shouldn´t the W has less cooldown, or make something like "While Living shadow from Death Mark is active the cd reduction of W from enemies struck by Shadow Slash is increase by 3 seconds instead of 2" or " After dashing through his target Zed gains 30/40/50% movement speed by the duration of the mark (3 seconds)"
Regards and peace.