The summary was published in 1945, and so must be relying on kill claims (which we expect to be exagerrated considerably when fighting over the other bloke’s country) rather than captured enemy sources. Even at that, the kill ratio claimed (fighters against enemy aircraft in air to air combat, so not quite the same thing as the RAND report’s single-seat fighters against enemy fighter pilots) is 4.3 to 1.
I did as advised and checked the US Bombing Survey. It is a big thing altogether, and I make no comment about what it say sregarding Japan, but the summary makes it clear that it is working from kill claims.
A brief internet search, combined with what I remember from reading Christopher Shores’ stuff, makes me think that the figures for the Pacific are at least as far out.
Just as interestingly, the claims for the Korean Air War seem even more contested. At least in the case of WW2, no-one doubts that the Allies did achieve genuine air superiority over the Axis powers: with reference to Korea, the Russians seem to feel they got rather the better of it.
Genuinely untangling all this seems like a real job of work though!