They can fly easily with our technology. A good way to look at it is the X-36, which had no vertical stabilizer. It still flew, and straight, though it had no large yaw-based control surface. The flight dynamics, then, work similarly with the VF-1.
I think Isamu was talking about a much more precise version of FBL to go along with the forward-swept VG wing on the YF-19. Perhaps, it even shifted weight within the valk to change the CG actively, increasing combat maneuverability, while retaining stability in normal flight.
Though, another problem I notice is at high sweep, the VF-1's wings are too far over the wing for the ailerons to move down, due to the engine nacelles. This would severely limit its ability to control itself at high sweep, sans thrust vectoring. Given, you'd be unlikely to see it at speeds low enough to warrant full range of motion.