...He listened to them equally, using them for different situations and finding a balance. That's how they won. If he's listened to Marco overwhelmingly and rarely Cassie, they'd probably still screw up. And vice versa.
That's the whole point of Jake, he's the glue. He holds everything together, without really offering any specific hardline skills of his own. Marco's strategic pragmatic nature tempered by Cassie's solid moral infallibility. Without Cassie's influence filtering through Jake, they'd be blowing stuff up and leaving David to die and whatever else. Without Marco's harsh practicality, they'd never accomplish anything. It's a compromise, a tightrope.
Jake's always been the middle-ground. Not as perceptive as Marco, as empathetic as Cassie, as headstrong as Rachel or knowledgeable as Ax or pure-natured as Tobias, he's the one who brings it all together. Jake's capable of both some pretty amazing and horrible things, but with the influence of the other's he's able to use that and make things work.