See a superb article by Abraham Ait at The Diplomat paysite about the inferiority of the F-35, titled "Why the F-35 Isn’t Good Enough for Japan" which argues in part:
"..While the F-35 retains some radar evading capabilities, its radar cross section is over ten times greater than that of the F-22 making it far less survivable — leading some analysts to term it a “pseudo stealthy” fighter. The F-35 has less than half the range of the larger F-22 and lacks the Raptor’s advanced long ranged air-to-air missiles, which for [Japan] an archipelago nation separated from its potential adversaries by vast seas are major shortcomings.
As a single engine light platform with a small arsenal of just four air-to-air missiles, restricted to a below average speed of Mach 1.6 and a very low altitude relative to the Raptor, the F-15J, and elite twin engine Chinese fighters, the F-35 hardly presents an adequate solution to counter China’s growing fleet of J-11 fighters — let alone more advanced platforms more recently deployed by Beijing such as the Su-35 or J-20. Indeed, it [the F-35] was never designed for such an air superiority role.
...With Tokyo unable to acquire the F-22 and with none of its allies producing a fighter capable of replacing its aging F-15 fleet, Japan sought to develop a fighter indigenously to fulfill an advanced air superiority role and match China’s latest heavy fighters such as the J-11D and J-20. The program, at prototype stages known as the Mitsubishi Shinshin X2, saw the first flight of its technology demonstrator in April 2016..."
"Abraham Ait is a military analyst and founder of Military Watch Magazine."
See the WHOLE EXCELLENT THE DIPLOMAT ARTICLE a Paysite well worth subscribing to.