I dont think its do with the weight to be honest. If AA would of hit Andre Ward flush, I would feel very confident that he would been capable of putting him down, hurting him, or knocking him out. Ward has been down against journeyman earlier in his career. I just think Dirrell let the cat out of the bag on how to deal with his style, that Froch and Ward exploited that.
Everyone already knew how to deal with Abraham, the problem was keeping it up for 12 rounds without getting caught. Froch didn't really do the same thing as Dirrell I believe: Direll moved and jabbed, Froch moved far less but bullied Abraham with a very hard jab. Yes, Wenger is useless but very well regarded in Germany apparently. All he seems to teach his charges is to keep their hands up. I've never heard him give good advice in the corner either, except "you're ahead on the cards" when in Germany. As an aside, I don't like the way he treats his boxers, he seems to always want to come across as their superior, always belittling them.
He'd never faced anyone on the level of any of his opponents in the super 6 imo. Froch is just braver, more offensive than Dirrell, he will press his advantage when he has success, Dirrell is too tentative and cautious to do that, so instead of punching more, like Froch, he will move more, but they essentially did the same thing, kept it long, utilized their ability to dictate range, as they realize AA has problems closing range.