In the aviation industry, any small change on air-frame needs massive calculation and experiment, that's why for Boeing 787 just the new Wings cost 1 billion USD.
For heavy fighter like F22, J20, even the DSI intake takes years of research, i can say AVIC inspired by LM, but can we say J20 also based on F35?
Thanks to China's world top level of supercomputer squad, AVIC would get J20, JF17, J10C, J31 done for those nice intakes supported by supercomputer's calculation.
You would compare how complicated mig1.44 and how clean the J20 just on intake, it reduce the complexity and weight remarkably.
I won't blame the people who just claimed the J20 is a copy of Mig1.44, it's might not because of the ignorance or stupidity;
I think it's more like commom Indian people are lack of industrial education and sense. I think India is still not a industrialized nation, that's why there are such strange ideas, it's just like Chinese were not educated the concept of industrialization and made stupid and huge mistake on 1960s', famous as Great Leap Forward.
When Indian aviation industry truly go through the whole process on designing and producing at least a 4th Gen heavy fighter, not purchasing, financing or waiting such project, they will know how hard it is.