You haven't changed my mind. If it's such an advantageous shape how come we don't see modern planes with that design?
The Flying Wing concept goes back to 1907 and survives as the B-2 stealth bomber and several other modern jet aircraft. It looks a lot more like Arnold's historic UFOs too.
I said it had one advantage, a short takeoff.
As for why the design didn't evolve with the jet age, I can just imagine what such a craft would do if it lost one engine. Not much room for the loss of symmetry, and I do remember that it was necessary to put, at least the prop engines, at the edge, for some forgotten reason.