Well if someone could theoretically reach 100% damage avoidance, I'm sure there would be quite a few very good uses for that, even if you have to walk away from the computer and grab a snack while you autoattack 150 epic elite mobs. Just because you can't hold aggro, doesn't mean the ability wouldn't be broken. It would just be broken in a really slow way.
To get back on topic
Cookies.
What do you suppose the owlbear cookies do or do not stack with? It's a rage bonus. Does that mimic barbarian rage? Would it prohibit casting in the same way? If it is basically a small barb rage, then it's useless for barbarians. That would make some people angry too I suppose.