Something that is supposed to be a simple answer. Confuses me even more. Just tell me in layman's term. Did they detect a J 20 deep in China's interior or not? If so, then China and anyone else is wasting their money on Lungberg lens or not.
Have you thought that, perhaps, the lungberg lens is the reason for being able to detect the J-20? Letting people know there's a big bad wolf in the area can be an effective. As can flying it through so it can be detected and then fly again - when they know you are there - and not be. Stealth gives you other ways if messing with your enemy or rival.