Their domestic turbofan engines are only just beginning to be equipped on their land based fighters. For Navy carrier fighter jets, the engines will have to be significantly more robust than land based fighters.
So their own engines aren’t as good as the Russian ones yet.
Distortion tolerance and corrosion resistance are well documented in the open literature. They'll get there.
It's a matter of time, like I said; eventually they'll catch up to the Russians and the U.S., as long as they prioritize the technology.
Take a look at the employees of the average U.S. engineering company. You'll see lots of their countrymen, and if you think they're all true blue loyal 'murricans, I have a lovely palace in downtown Beijing to sell you.