I'm hoping this improves...

[Pantalaimon]

So if you're already up on them, and have to be to kill them, it's not a good thing.  Particularly when you seem to think that the best thing to do when a monster is in your face is try to cast fireball repeatedly.  *shakes fist at annoying party* 
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You're pretty much bang on. If there's no tank and you're a cloth type, and the group is badly organized, your best bet would probably to mentally go "screw aggro management" on ONE of the mobs. The frost nova thing managed to give you aggro of all three, whereas had you just gone crazy with fireblast/AM on one of the guys you'd have one in your face and your party'd be dealing with two in their face. Much better odds.

(This is basically what Skan's saying :P )