Please clarify this part.
If you look at the J-20 you see a F-35 with foreplanes and weaker engines from Russia.
Now most countries have been not privilaged like China has been by US administrations, the accces to American technologies via tech transfers if they want to operate in China.
Ask your self why other countries take longer to develop those technologies?
The Americans have been aware that most technology will end up in the hands of the Chinese military and the europeans too.
They know each time the Chinese export something sooner or later some revenue and profit will go to the Chinese military.
Do you think Trump is the first US president aware of that?
Do you think the Chinese are so smart to cut 50 years of aviation technology and secret research in 20 years?
Only a moron thinks the Chinese are advancing without a real political sponsor and geostrategic planning.
The answer is China has been allowed to follow into the trap, because the only two geostrategic rivals the USA has are China and Russia, and both have to be dealt, the trap is set, China will fall for it, and it will be crushed.
The reality is american research is much higher, and Europe too.
Not only they have more stealth aircraft. but they need a rival to justify spending in weapons but they need allow Chinese cockiness to re-direct Chinese anger towards Russia.
Remember the German-Soviet pact, only that, China is not ally of Russia.
Story repeats it self