J-9 or MIG 1.44 ?
If we go by public information, the J-9 project was cancelled due to severe technical and social disruptions that hindered its development, but high probability it was the Cultural Revolution that placed the most stress on the program.
The argument that the J-20 came from the J-9 is more likely from the reasoning that the J-9 is an indigenous project than from credible technical analysis. All engineering projects, no matter what, from a new tire tread to a new jet fighter, designers and engineers FIRST looks for precedents. If anything, it is to make their work easier little by little. Why design a new airfoil when I can peruse the NASA/NACA database to see if there is anything I immediately use or use with as minimal modifications as possible ?
The 1.44 project is 25 yrs younger than the J-9 project. Further, the Soviets are more renown than the Chinese when it comes to aviation. We may not know the technical details of both projects, but given the history of Soviet/Russia involvement in aviation, it is a reasonably educated guess that the MIG is more technically sophisticated and probably more complete in final design than the J-9.
So if I am going to design a jet fighter based upon my current resources and time pressure, between two precedents, why should I use a project that is 25 yrs older ?