Just to clarify, you believe that Grievous Wounds is currently too accessible and for that reason must he "nerfed" by making it a keystone mastery?
Grievous Wounds is not too accessible for anyone with the exception of maybe AP mids who rush Morrellonomicon. AD champions have to build the alternative to LDR, and unless they want to be walking around with an Executioner's Calling taking up inventory space, they're heavily investing in % bonus armour pen, which isn't terribly useful early on in many cases.
If you can effectively rush that item (IE, the enemy is building a lot of armour and has a lot of sustain) then that's all it is; a situationally effective item. That doesn't make it overpowered. If champions existed that could have a massive amount of defensive stats with a massive amount of sustain and there were no items to deal with it, that would just be absurd.
Tanks and fighters are one of the most problematic classes and are almost never weak when people claim that they are. They're just not always as brain dead to play as people expect.
It sounds like your issue is more getting rid of Warrior's Blood Lust than anything else. In that case, yeah that mastery is a little silly. However, reworking an entire stat is definitely not the answer.