This is why I use Mindbender on Beastlord, with AS, instead of Insanity. There is no point in doing poor AoE on pack adds to pad meters when using those globals to maintain dots and putting MB on boss will give better results.
However, Blackhand. I would agree to using CoP to a certain point. Right now the 25th highest world dps for all classes on Blackhand HC is a Shadow Priest using AS. Suffice to say it's the number one Spriest by far on that fight. AS is still very viable on those kinds of fights, if you have enough crit.