Sorry if this has been repeated, but I couldn't read everyone's post...
The Japanese had a different philosophy about a pilot. They emphasized personal skill almost to the point of acrobatics. This influenced plane design and tactics. So while I cannot comment on the specific structural integrites of various models, I think it is fair to say that Japanese planes were more manouverable at the expense of some other attribute (be it armor, armament or speed, etc..)
As several people have mentioned, quality control on the manufacturing coupled with limited availability of spare parts led to many structural failures and limited flying time for almost all models late in the war. The NIK and Ki-84 both suffered landing gear problems. I think I read as high as 25% attrition just due to landings for one of them. I'll check my figures at home tonight.
Also, I believe that the Japanese did not have the rotation program. A good pilot kept flying until he died or got captured. American pilots rotated back home to train the next generation. So Japanese pilots were generally less well trained than the American pilots by war's end.
I also think American tactics and engineering were evolving and improving during the war...i.e. things got better for us. The Japanese planes were often grounded or flown by inexperienced pilots, so things were getting worse for them. We are probably left with the memories of the end of the war, when things seemed to be going well for us.
Anyway, some generalizations, I know...but it's just how I read the judgements of Japanese vs. American planes...
