If I may, a missile like the AIM9x would be ideal for low RCS aircraft such as J-20, SU-57, J-31 or some ‘stealth’ drones where the F-35 would be unlikely to detect and lock onto those aircraft far enough to use an AIM-120 like it would for conventional aircraft.
There is also no guarantee that the F-35 would not be caught by surprise, during such wars as the Gulf War, Iran Iraq war, Vietnam War, as well as many others wars Migs, Mirages, F series fighters, etc would catch the enemy off guard, usually by flying low and avoiding radar and then climbed and engaged enemy aircraft.