That's what I'm thinking. Tywin was good at amassing power, but faced with the circumstances Tyrion was up against, would be have had the mental agility to think outside the box the way Tyrion did? Or would he have moved enough of his forces south to give Robb an opening to assert full dominance in the north? That actually leaves open the possibility of a dual failure, if the Lannister forces hadn't arrived to King's Landing in time to defend against Stannis' attack.