You have to remember the whole reason behind the F35 program is to be able to meet current threaths.
By the 1998-99 Kosovo operation, it was obvious the current generation of planes, F-15/16/18 were getting long in the tooth, Serbian air defences were able to furstate a lot of missions and the Serbians were not even using the best air defense equipment available at that time.
The F35s were designed to be a lot more "stealthy" so that in the event of a real hot war, whether against Russia, China or whoever, the F35s could fly at night undetected by radar and take out any air defences so that older planes like F15/16/18 could go in and bomb other targets.
Current gen ACs like the F15/16/18 are fine if you are going into an operation in a third world country like Afghanistan where there are no air defences, but would probably suffer heavy casualties in a war against a 1st rate power.
Yes the F35 is expensive, but as has been shown throughout the history of mankind, the cost of building a strong defense to dissuade potential adversaries is cheap compared to the costs of an actual war.
__________________
|