“So aren’t the P-51 and F-86.
Should we keep buying them?”
The P-51, Yes. They would be amazing close air support attack aircraft.
Seems to me there would be a role for piston engined close support aircraft. Being less expensive, they could be produced in higher quantity -- serving as efficient "bomb trucks".
However, wouldn't a modern version of the P-47 be better equipped for this job? The air-cooled engine would be less vulnerable to small-arms fire than the liquid-cooled engine with radiator on the P-51.
Or better yet -- fire up the old AD-1 Skyraider line.