To me it is not that much important. Working with Sukhoi kits given Chinese an idea on that is it a 4th gen fighter aircraft but they still unable to reproduce it’s 4th gen engines which is a 70s technology. At some point things are getting too advanced to copy&paste, you need complex knowledge to make it work.
China is decades too far from the edge which is a 5gen aircraft today.
Catching up with the West will likely take another 30 years (as the West isn't idle in development). But I do believe catching up with the Russians, i.e., can be done in about 10 years (I admit, I'm guessing here).
But its not like China don't have a jet engine available. But its not as durable as the Russian engines. An engine is made up of many parts rotating at tens of thousands of rpm's. And operating under intense heat and pressure. So, somewhere in copying, I'm sure the Chinese overlooked something that would allow it to last longer.
But I am confident they will find it. The challenge isn't catching up with the Russians. The challenge for China is catching up with the West in military technology. And that includes more than just engines, but integrating the high tech precision guide munitions to integrating land, sea and air systems. For all three to communicate in unison, etc. And to integrate it all via satellite technology. That, I believe, is where China's real challenge is. Not duplicating Russian engines.