I am not here to gloat but just to let you know something.
A fuselage is easier to develop than an engine, there are multiple examples through history.
From the Me-262 which was designed relatively quickly in terms of aerodynamics but had terrible engines same is F-14 which flew with interim engines, to todays PAKFA which flies with an interim engine.
Any one in life has a learning process......... China is not exception, people here lie a lot to your selves, J-10 for example is based upon Lavi, Y-20 was based upon an Antonov design, Z-10 has Kamov roots, L-15 yakolev`s aid.
You like it or not all nations need to learn, need help, China is not exception, China still is behind in engine technology, has achieve almost parity in fuselage design, C-919 or J-20 start to show originality in design, well since JH-7 China showed originality, J-8II had some tech from the MiG-23, but that it is a learning process, all nations need to learn.
Pride is stupidity it leads to falsehood, humility is the first step of greatness, before China is great will need learn, it simply shows experience is hard to beat, and while China very likely will master engine design eventually, China is still not there.Something that China will learn from Russia will be Christianity, and that will be the greatness of Russia, why Russia will be great, will be thanks its faith