I feel like Yasuo is a better Juggernaut than Morde...
You have your two item power spike

- sustain/tank

Well but then you have even more, because high mobility, and a cc while still getting a passive shield...
To top it off, you also typically only get 3-4 items in a full game... and he out scales morde late game anyways... so...
all pretty much make zed a pain in the ass to play.
which help survive early. Zeds only chance is to get a kill pre 6 vs Kass if he wants to win. Knowing this as a Kass player it is easy to give up cs, call out Zed roams, and force Zed's hand. Kass also more times than not Takes TP, and can play safe and TP back to lanes when he is low with that CD. If Zed takes TP he most likely will not get a kill Pre 6 on the Kass, if he takes ignite he cannot match his late game split pushing. Also you can
(and Two def items of your choice) is Surprisingly Tanky. He will have 100% crit to do some great damage, a Focus shield that scales well with Def states, along with a good HP pool. His ult provides any armor pen he may need, and a Windwall to block a good chunk of damage and CC from ranged Champs. Add a
is a far stronger build than frozen mallet. Sure you lack the slow, but you dont NEED the slow as yasuo. your Q is spammable.