Almost the death of the IJN...they still had enough to kick our butts at Savo Island a couple of months later, and continued to make life tough for another six months to a year, but...I do think Midway spelled doom for japanese military aviation.
They continued to throw their best pilots back into the meat grinder until they were all gone. We rotated our best pilots out, and over time, that was the difference.
Even as early as the battle of the Eastern Solomons or Cape Esperance, gunners on ships noticed a clear change in the quality of the Japanese pilots they encountered, fighters, bombers and torpedo planes. Earlier in the war, they had been tenacious and good. They became, even that early, much less persistent and noticeably less capable.
One thing I recall from Saburo Sakai’s book is he considered the American Pilots early in the war to be of really high quality but their planes were very inferior.
I also remember him saying the best pilot he ever faced was a Dutchman very early in the war. He was flying an old obsolete fighter but every time Sakai was ready to shoot, he would evade. He eventually did shoot him down but Sakai clearly thought he would have lost to him if the Dutchman had a good plane.
Sakai also said the reason the Americans eventually prevailed was the quality of their planes fairly soon became better than the Japanese. He said they did develop some fighters which were just as good as the mustang but they were too few and too late.