The US doubts whether it is expedient to further develop F-35 fighters, as the aircraft has essential deficiencies. According to the American Thinker magazine, 'ten years after the F-35 first flew, it remains in development, though 180 have been built. None of those aircraft can operate in combat; all will have to be modified if and when the final design has been settled on. There is not much point in doing that, because the F-35 has a number of show-stoppers that would kill it instantly in a rational world.'
It should be also noted, that 'being designed as a light bomber, the F-35 is less maneuverable than fighter designs up to 50 years old and will be shot out of the sky by modern fighter aircraft.' The forecast says the Su-35 is expected to be able to shoot down 2.4 F-35s for every Su-35 lost. But even more terrible fact for the Western Air Forces is that they see the F-35's vulnerability now, when it has not become operational, and by 2020 stealth PAK FA fighters designed by Sukhoi will enter service. Still, there is enough time for the Western fighters' pilots to change their profession into another, more safe carrier.