Crit has always been better than mastery. More so on single target and large aoe packs and less so when cleaving with havoc. No matter how you look at it you aren't gonna find that many small cleave packs in CM's so that gearing purely for havoc would be worth it. Even if you had only small packs it wouldn't be worth it since you'd be better off with more crit and more embers to get off more CB's and SB's.
Don't know how people have started justifying mastery over crit when there's no evidence to back this up. I agree that there's no point with crit enchants if you play all specs but purely number wise for destro crit is so much stronger.