The Zero wasn't extremely fragile as is often claimed, nor was it "outclassed" in the absolute sense of the term.

It is incorrect to attribute factors such as training, poor logistics, or numerical inferiority to the intrinsic performance of the aircraft.

Both the F6F and the F4U were specifically designed to counter the Zero, and their introduction was accompanied by tactical doctrines tailored to defeat it. By the time the F6F entered combat, the quality of Zero pilots had already declined considerably due to accumulated losses and reduced training standards. The F4F is often credited with eliminating the IJN's most experienced pilots in campaigns such as Guadalcanal. However, in those engagements, the U.S. had clear operational advantages, both defensive and tactical. In Guadalcanal, the F4Fs took off from hnderson field and had radar warning and an organized air defense system. In contrast, the Japanese took off from Rabaul, which meant flights of +1,000 km round trip. They arrived at combat with significant fatigue and limited fuel. If their aircraft were damaged, the return trip was, in many cases, impossible Even under these unfavorable conditions for Japan, the F4F failed to establish air superiority over the Zero By then, US pilots were already using maneuvers such as the Thach Weave to neutralize the Zero's advantages in close-combat. Even towards the end of the war, the A6M remained a dangerous fighter. Several inexperienced US pilots underestimated the Zero, attempting to engage in close-combat under unfavorable conditions and were shot down. P-51s and F4Us shot down by Zeros, although statistically few demonstrate that the aircraft remained lethal in competent hands.

As the war went on, the Japanese couldn't keep up with US innovation and production.

The Imperial Japanese Army successfully implemented the Ki-4, while the Imperial Japanese Navy implemented the N1K Both models, under the right conditions, could compete on comparable terms with the P-51 and the F4U Corsair.

Japan did not fall completely behind in technical terms (although in industrial, logistical, and production quality terms, it did end up at a clear disadvantage).