... but wow it says something about the Japanese airforce.
It does but we generally view Marseille's claim of 17 Western Desert AF a/c in a single day (more than one sortie, though) as impressive and are perhaps less likely to say 'wow that says something about the RAF' in the same way, though it does. The Germans in the Western Desert 1941-42 held a consistent advantage over the British in fighter-fighter kill ratio, perhaps greater than the kill ratio enjoyed by USN fighters over JNAF fighters in 1944, actually.
Allied records indicate Marseille's claims of Sept 1 1942 were probably mostly correct (see "Fighters Over the Desert" by Ring and Shores), what of McCampbell's? It's harder to decipher in a larger combat, but here's some info:
The formation VF-15 intercepted was probably part of the main morning attack by land based JNAF a/c of the 2nd Air Fleet on Luzon against the US carriers to the east. Hata and Izawa "Japanese Naval Aces and Fighter Units in WWII" quote this force as consisting of 199 a/c; the detailed OOB in link totals a little less but agrees with H/I that it included 126 fighters; given as strike unit of 36 Type 99 Carrier Bombers (Val) plus 6 bomb carrying Zeroes of 221st Air Group; escort unit of 26 Zeroes of 252nd AG, 28 of 221st AG, 21 Shiden ('George') of 341 AG; covering force of 51 Zeroes of 203rd, 653rd and 634 AG's. 12 Susei (Judy) attacked singly (one inflicted fatal damage on CVL USS Princeton). 11 Tenzan (Jill) took off after the main wave of bombers and fighters.
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341st AG link:
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McCampbell led 2 divisions of 7 total a/c; one F6F of his own div failed to launch; then initially all five others including Slack of his own division attacked fighters and bombers below (claiming 4 Vals and 2 Zekes, though also Oscars and Tony's prob or damaged) while McCampbell and Rushing took on fighters above; later Slack rejoined and the three claimed altogether 13 Zekes, 3 Oscars, and 3 Hamps (5 Zeke, 2 Oscar and 2 Hamp by McCampbell). VF-27 also had a large scale combat with Zeke/Val-heavy formation at around the same time, as well as encountering twin engine a/c not explained by the OOB above; VF-19 and -44 also made claims in the same area and time. Claims against fighters of the three squadrons totalled 39, including 7 Tojo's (probably Shiden) and 4 Tony (also Shiden? JAAF and JNAF a/c together on offensive missions was relatively rare), so 52 Japanese fighters were claimed destroyed including VF-15's claims. This is separate from many USN claims that morning on scouting/sweep missions (divisions of F6F's used as scouts) over Luzon that morning which may have been JAAF, and also included twin eng a/c so not likely the strike force described above.
Hata and Izawa state (or assume) McCampbell engaged the 252nd AG, but don't say how they determined this. Actually, though perhaps coincidentally, the 221st and 341st accounts (see links above) both say they engaged 7 F6F's. The 221st lost 8 pilots (per link), the 252nd lost 11 a/c (per HI), 341st lost 9 a/c (link), 203rd lost at least one pilot loss named in HI, I checked original record for this day but it's missing; 653rd original record for this day only describes its ops from carriers, it had already suffered heavy losses in October and only part was operating from land; 634th lost 8 a/c (HI). So, if only the claims mentioned explain those losses, the claims were quite accurate; though that's a fairly big if. Altogether H/I say the JNAF lost 67 a/c including non-fighters and probably including other smaller raids. There's no question the VF-27 and VF-15 F6F's inflicted a lot of damage on this morning strike, though, and seems likely McCampbell scored some serious % of 9 kills, at least.
Joe