Stand off weapons need targets, and their range isn't endless. J-36 is exactly the means to find(and prosecute) those targets in enemy rear.
What enemy "rear" are you referring to?
Every point in Japan is within 1300km of mainland China and within 150km of an ocean approach.
Why you build it if you don't?
That's the question that apparently killed NGAD-1, by the way.
Current generation stealth fighters with tailfins can be detected at long range with low-frequency radars,
So broadband stealth is simply the new standard.