[GuerraCivil]

If I have understood correctly the Japanese fighter pilots had to keep the drop tanks even during the combat over Guadalcanal in order to have enough fuel reserves to fly back to Rabaul or other Japanese airfields like the one in the Buka island. This must have been some handicap in the combat situation - drop tank means extra weight, more drag and less manouverability in combat.

Taking in account all the circumstances and the Japanese handicaps the real question is not why Japanese lost but how Japanese managed to keep pressure on Guadalcanal as long as they did.

The biggest problem in the Japanese strategy at the Pacific was that it was too ambitious for their limited resources like the inadequate logistics and maintenance structure.

By mid 1942 Japanese were already too overstretched to make any further progress and they could not replace their losses as easily as the US and its allies. Even when the air victory records were relatively good for Japanese, the relative losses were much higher for the Japanese side. A Wildcat shot down over Guadalcanal could be repaired or used for spare parts and its pilot could save himself by bailing out or making a belly landing. A Zero shot down was completely lost as well as its pilot.

One should note that by late 1942 Japanese were still relatively strong and could win some battles like in the Santa Cruz on 25.-27.10.1942 which to my knowledge was a clear tactical victory for the Japanese. I would dare to say that by late 1942 Japanese pilots and their planes were still quite competitive with their US/Allied counterparts although the balance was already favourable for the Allied side.

When one takes in account the US/Allied opinions of the "inferiority" of Japanse fighters pilots in late 1942 one should remember the common overclaiming factory, of which following examples of the air combat records over Guadalcanal:

24.8.1942 - US combat claims on 11 destroyed Japanese bombers and 5 destroyed fighters - real Japanese combat losses: 3 bombers and 1 fighter

26.8.1942 - US claims: eight bombers and five fighters destroyed - real Japanese losses: 3 fighters

Between 18.-23.10.1942 US pilots claimed to have destroyed as many as 50 Japanese fighters whereas the actual Japanese losses were 12.

Source: F4F vs. A6M Zero Sen - Pacific Theater 1942 (by E.M. Young 2013)

This kind of combat records (made in perhaps good but erroneus faith) must have added something on the comments of the "deteriorating combat skills" of the adversary....