The sale of engines was perosnally authorized by putin even after immense indian lobbying. The next batch will carry WS13 chinese origin engines which will also be used in export variant as the Russian are not happy about their components falling into their direct competitor market. Also there are talk about integrating western engines most probably from GE since Pakistan already maintains F-16 it will be easier for them to continue on common origin platforms.
As far chinese manufacturing capabilities, it has the largest high-tech and precision electronics fabrication facilities, something which soviets todays russian lack a lot. Large part of chinese copying comes from electronic fabrication contract outsourced to them by Russia. The chinese have built their defense industry over consumer electronics and dual use items to bypass sanctions. For example, Chinese missle system sold to Iraq which used a Company PC system as C&C console.
The real sphere where Chinese serious lack behind is composite materials, nanotechnology and their manufacturing however with chinese students making largest talent pool in western universities this is likely to catch up fast.