I agree, engine technology is difficult to get right. However China is different from the Soviet Union/Russia. They have thousands of Western trained scientists and engineers, greedy corporations have setup high tech manufacturing in China in order to get market access, and China has a $hitload of money, all things which no potential adversary has had for a long time. They will master this technology far faster than you think. If their new airframes are decent then good performing engines will be a problem. Also, let's not forget they have the most computer users, the most spies, and most of the world's exotic rare earths all of which will benefit their huge electronics industry and the material science industry needed for high performance military jet engines. We can thank Western greed for this nightmare scenario (along with Japan).
With the Ukraine crisis going on, China will be watching Western reaction very closely. Their neighbours are as well because all of their South China Sea assets are looking very vulnerable now.