The exodus didn't fail completely, Rasputin's strategy of spreading out is the only reason we have Awoken. Without the Awoken being able to intercept the Fallen and warning us of Oryx, the City would have fallen. It was the Dead Orbit fleet that told the Vanguard about the Cabel breaching the Dreadnaught. FWC says they're about getting ready for war, but it's the "cowardly scavengers" that put their neck out on the line to keep the fight from getting to Earth. Keep looking into your crystal ball all you want, I got patrols to do.