America does need to respond to Chinese technological advances in air power:
The IISS [International Institute for Strategic Studies] declares that China has become an innovator in military technology and is “not merely ‘catching up’ with the West”.
They are getting close. But remember that the J-20 cited is actually a frontal only stealth plane--and has other deficiencies.
More to the point, air power is not simply the result of the plane technology.
The Air Force is a system of air power that includes planes, crews, logistics, and the entire system of working with all the various pieces of the Air Force to apply air power, and to work with other services to provide them with air power. The Air Force has decades of experience built on actual wars back to and including World War II around the globe in various conditions.
China can't match that experience or system.
Not that I'm dismissing the Chinese technology. But even our retired F-117 was a fully stealthed plane. China has not deployed that type of technology yet.
So react with a sense of urgency to China's new technology. But don't panic. The Air Force (and Navy) systems are still better.
UPDATE: The J-20 has problems. If we had similar problems with one of our operational planes it would be a procurement scandal.