Which was clearly the case in WW2.

And _might_ be the case if the confrontation with China is proxy wars. Hundreds or thousands of spare units (of tanks, AA, helicopters, fighter jets) would be useful in Ukraine, for example.

But it's hard to see a use-case for hundreds of B-2s, for example. By the time those things are flying in anger, twenty or thirty will do everything you're ever going to do.