Maybe "worthless" wasnt the best choice of words, but 50%- to 20% is a huge blow unless you are stacking all resistance gear. I have a friend who uses crushing advance, he likes it. I think its cooldown is a bit long however.
I can't help but feel like you're missing the essential context of this nerf: All enemy damage is being lowered in amounts exceeding what would be required to simply offset the nerf on the ability.
Meaning: Post 1.05, with Warcry: Impunity you will take LESS damage than you do currently. If you don't use Warcry:Impunity, you will take LESS damage than you do on live. Basically if you already don't use Warcry, you will take less damage in 1.05. If you already do use warcry, after 1.05 with war cry you will take less damage.
No matter how you slice it, you take less damage in 1.05 unless you use war cry now and drop it in 1.05. Anyone who stays using it or continues to not use it will take less damage.
Therefor: Ability nerfed, Overall survivability buffed.