Appropriate Zed Nerf?

Currently, Zed's ultimate does damage from a percent of all magic and physical damage dealt. This is simply for certain actives and also for his passive, which does 6/8/10% target's max hp as magic damage. What I propose as a nerf due to Zed's insane synergy with Duskblade, is that his ultimate no longer does damage from his magic damage dealt - this means that a percent of the physical damage dealt is how much his ultimate would do. This removes 3/4/5% max hp damage from his ultimate combo.

Tell me how you would feel about this change, and if it is appropriate to balance Zed out.