China stopped using the AL-31s and AL-41 and has been using the WS-10C, to its safe to say they have some degree of confidence in it. Now the WS-15 has been developed which a leap for China, I don't think engines are too much of a problem for China anymore. They are still behind engines like the F135 and the Pratt & Whitney XA101 in development, but they acre caught up to F119 more or less.
The WS-13 is not much of an upgrade compared to the RD-93, there is an improved WS-13E as well, but I guess Pakistan has continued with the RD-93, might be b/c its easier for logistics or b/c we haven't really seen any testing in a single engine configuration. The WS-19 is the one where China finally catches up, and its very close to the finish line.