In actuality a B-29 training mission wasn’t that safe. Twice as many B-29s were lost to engine fires and other non-combat operational issues than to Japanese fighters and flak.
The “Silverplate” B-29s had new fuel-injected engines, reversible-pitch props and were maintained by an elite team. Late in WWII, it may well have been safer to be in a Silverplate B-29 over Japan than in a regular B-29 on a training mission, but not exactly for the reason implied by LeMay.
Altogether than quote is problematic. B-29’s had a quite high operational loss rate in early training and operations. But that was improving by late in the B-29 campaign, fleet wide. It was better still after WWII (for example in Korea) though operational loss rates were still horrendous for even very reliable WWII/Korean War ear a/c by today’s standards.
The other thing it points to is that the 267 B-29’s the 20th AF counted as lost to ‘other causes’ on combat missions (as opposed to training losses) seems to have included a significant number of a/c damaged by fighters or AA but which didn’t go down over or near Japan, but made it back a significant way to the Marianas or crash landed there. Or where cause was just unknown, but with benefit of Japanese accounts it can be seen to have caused by fighters (that’s true of the a/c I mentioned above as the last down by Japanese fighters, due to a fire of unknown cause in the USAAF Missing Air Crew Report for that plane, but credited to a particular night fighter unit on Japanese side). So the 74 to fighters, 19 to AA and fighters and 54 to AA is probably an understatement, and the 267 were not all to non-enemy action causes.
Doesn’t change the big picture of relative ineffectiveness of the Japanese defense throughout the campaign or in particular to the fall off in Japanese fighter activity from spring 1945 to save fuel for the anticipated invasion.
A number less subject to interpretation is the 20th AF stat quoted by Coox in “War Against Japan” that the average B-29 mission (not sortie) encountered 7.9 fighter attacks in January 1945, 0.3 by June.
AIUI, the two bomber missions were simply a calculated gamble, betting that the B-29s would make it there unscathed. If the Japanese sent fighters to intercept, there was little the bombers could do but say “Ah, fuck” and take whatever futile evasive action they could.