Original sentence: The Arrow was far from the only heavy high-speed interceptor design canceled at that time; both the Republic Aircraft XF-103 and North American Aviation XF-108 Rapier, both of which were slightly more advanced than the Arrow, were cancelled at approximately the same time
Edited sentence: The Arrow was far from the only heavy high-speed interceptor design canceled at that time; both the Republic Aircraft XF-103 and North American Aviation XF-108 Rapier, both of which were far more advanced than the Arrow, were cancelled at approximately the same time