It wasn’t meant to weaken him. It even says in the patch notes that they wanted to maintain his damage but remove that instant tank kill ability. I’ll dig up the patch notes once I’m home.
Developers Comments: The goal of these Hanzo changes is to allow him to have new options and maintain his high damage output, while removing the frustration of fighting against the old Scatter Arrow. Hanzo is now much more mobile with his new Lunge ability, and with the combination of the bow projectile speed increase and the new Storm Arrows ability he can now deal his high damage more consistently than ever before.