Thing is, AEW&C can detect the J-20 at 300-400km. If we assume the E-2D Hawkeye has 600-800km detection range vs 0 dbsm, and the J-20 has -10 dbsm in UHF frequencies, then it can be detected at 300-400km ranges. Assuming that a derivative of the PLAAF's interceptor missile is readied for the J-20, how many missiles can the J-20 carry? And considering the bulk and weight of the interceptor missile, how many anti-missiles can the OPFOR carry in return?
Meteor, for instance, sports a 300+ km range and weighs 185 kg. The PL-ASR, on the other hand, weighs about 90 kg. This implies that for a single interceptor missile, the opponent can launch 2 anti-missiles, and what's more, if the opponent keeps 4th generation aircraft as escorts for their AEW&C, the defensive payload can easily hit 64 or more per AEW&C.