We need to see what will happen in the future mate.....I see that your J31 has become J35 and it needs at least another 5 years to complete its development according to your own official.Fighters are way more complicated. Experience is very very important in this aspect. The only comparable East Asian country in this field is Japan (Type Zero, F-2, Shinshin, and F-3 in the future, meanwhile C-2 transporter is also a masterpiece, though all Japanese products are irrationally expensive), Korea is no player, the success of TA-50 relied more on LM rather than Korea.
As for SAC, it is dedicated to produce fighter planes for more than half a century, and they do designed J-8.
J-6, J-7, J-11, J-15, J-16 are all produced by SAC.
The "license built" only applies for J-11A, which is totally assembly-work. From J-11B on, it is we that control all the production, everything is our own except the AL-31 engine (will be replaced by WS-10 in recent years), thus upgrading and personalization is all at our own control, that's why J-16 come into birth. The only restriction is we can't sell them to foreign customers since we use AL-31 and nothing more, our avionics are even more advanced.
That's why SAC can design and carry out FC-31 so quickly --- the experience in fighter manufacture, not only some "license built" but whole flow. 60-year experience of R&D is not just paperwork, but real output.
Again, the first flight of prototype of FC-31 (No.31001) is 8 years before, mean while there is no plane seen for TFX/KFX for years, that is the gap.
And don't forget SAC and CAC is both under the control of AVIC, they are in the same incorporation controlled by the state, they all serves China rather than stakeholders, so the technology on J-20 can also be applied on SAC's product. FC-31 is not a product only of SAC, but AVIC, you must make clear of the difference.
For KFX, whether it will success or not depends on LM, not Korea and Indonesia, and I even doubt whether there will be a result for KFX project --- it will cost tens of billions of $$. Korea has purchased F-35, and its economy is declining, they may not have the money to develop KFX. What's worse, US produces are a good but greedy cooperator, our Super-7 (the original project code of JF-17) had many economic problems when cooperated with Grumman.