Well if the Indians didn't have enough time to learn from Kurt Tank on fighter design, then what about the Chinese learning how to build the J-7 from partial collaboration with the Soviets?
Solving J-7 took China like 2 decades, and was rather controversial (independent attempt to go all-weather interceptor route never really worked out, for example).
But J-7 wasn't there in a vacuum (J-6 was there, alive and kicking), and more importantly, process was gradual and staged: Vanilla J-8 isn't exactly a step too far from J-7, nor is something like J-7E.
Tejas was born far too late for Marut expertice to transfer, and was far too much of a jump (Marut is,
at best, J-6 level aircraft, and after that Indians decided that they're good to directly jump to aircraft far more advanced than M2000), with own engine, radar and everything. Everything was in addition to rather unhealthy climate (China fights mostly proxy wars in the air, and is nuclear; India isn't nuclear, fights directly and can't really afford being late).
Furthermore, China remembers well being chocked between early 1960s and late 1970s; India always had international aid to rely on.
Frankly speaking, it's a bit of a miracle (and persistence) anything worked out at all - such projects usually fail altogether.