If you're doing this for more than 2 mobs, you're doing it wrong. Mangle is a threat loss on mobs compared to swipe, and while it does boost maul threat it doesn't do it so much that it makes up for the loss of threat on swipe. To put this in perspective - every time you mangle you do about twice the threat that one hit of swipe does per target. With three targets, swipe does overall 1.5x the threat of mangle.
Also, if you are having problems with AoE packs, you should be swipe/maul'ing and then tab target mangle'ing mobs. So Mangle swipe swipe, tab, mangle swipe swipe and repeat.