The biggest problem with the F35 is the Chinese stole the plans and copied it to make the J31. They did the same with the F22. So China does what it always does - steals others IP and copies iy.
https://eurasiantimes.com/f-35-vs-j-31-can-chinas-stealth-j-31-aircraft-match-us-f-35-fighter-jet-blow-for-a-blow/?amp
