You think that some Song generals wouldn't have defected to the Mongols at some point? The Mongols were famous for their spy craft and intelligence service, and

You think that some Song generals wouldn't have defected to the Mongols at some point? The Mongols were famous for their spy craft and intelligence service, and for being able to convert key enemies when necessary. And calling their tactics "hit and run" is a huge oversimplification, as is the rest of your points.