Everyone points to the Xbone reveal as the beginning of the end for the Xbox brand, but it started earlier than that. Really the first big crack that began to show was with Don Mattrick trying to chase the Wii's success with the original Kinect. Look at the games Microsoft were funding pre and post-2010.

I'd say Peter Moore could've saved them had he stuck around but the RRoD was on his watch, so who really knows.