Lets suppose the YJ-12 is real and the JH-7Bs can carry two of them each. 400 KM is well within the range of carrier aircrafts armed with AIM-120s, also traveling at Mach 4. A carrier borne E-2s can detect targets out about 550 KM. Which will provide early warning for the carrier, which receiving the threat warning will then launch a "whole lotta" F-18s/F-35s in the air "real quick" and also prompt the fleet air defense ships like the Ticos and the Burkes to get in position to launch their "whole lotta" SM-2s.
The outcome of this scenario is that a few YJ-12s might get through but not a lot. But I guess the PLNAF will then launch its second squadron of JH-7Bs with another 48 YJ-12s ...