For the all-melee classes, it is important to remember that if the mob is facing you, parry/block chances are much higher. This is especially tough on warriors as they don't generate rage when blocked/parried/dodged (or mine generate much less at any rate). I usually switch to my prot spec for the initial aggro so I can turn them away from the 3 Arms guys, which makes things much easier. Once they're all green, it's less of an issue though it seems to me that time-to-clear is definitely better with good positioning.