[GuerraCivil]

One often forgotten factor is that the medical supplies and maintenance reserves of Japanese frontline units in the Pacific were less than those of the Allied units. For example many Japanese fighter units lacked quinine or other medicines to treat malaria - this was a big problem already in 1942 when Japanese supply lines were already over-stretched. The situation got worse with time when Japanese supply lines came under growing pressure and were often cut by the continuing sinking of Japanese cargo ships by US submarines and aircraft attacks.

At the average level Japanese pilots were more sick and less supplied than their Allied counterparts (who also suffered considerably of the trophical diseases). Many otherwise well-trained and experienced Japanese fighter pilots had to climb to the cockpit of Zero (or Oscar) being ill and almost all Japanese pilots at the South Pacific were weakened by malaria. I have read about some pilots going to combat even when they were suffering of fever. Perhaps this was not so much of stubborn "samurai/banzai" attitude than a reflect of the grim situation when even sick men were forced to combat by their superiors.

You can hardly expect them to have been in top-form in air combat - the sick man in the cockpit is slower to react in combat situations and his instincts are less sharp than those of the healthy (or less sick) pilot.

This may have been a considerable handicap for the overseas IJA/IJN units in South Pacific and one of the very reasons why the combat skills of Japanese pilots seemed to go down already during the mid/late 1942. When it comes to the training level and average skills of IJA/IJN pilots by late 1942/early 1943 I guess that they were still higher than by late 1943 and 1944.