Fighting a war against China (presumably over Taiwan) doesn't seem like it would have much to do with national security.

That aside, people are simply not able to model how the next peer conflict will be fought ahead of time. All sides will be learning as they go. Building complex systems like the F-35 seems like a good way to maintain engingeering/technology culture that can be adapted when the time comes.

Also, I'm fairly skeptical of China's military. They keep purging people, and the human element in war seems underrated.