Something I don't quite understand here.
China has the WS-10a for its j-11b(d)/j-16 and recently the "b" version for its single-engine j-10b/c so how is it that the lower thrust WS-13 this long? Priority issues? Or just a case of certain firms not being as good as others?
Funding, personnel and the sheer number of engine programmes running in parallel.
Even companies and nations with decades of experience at the very cutting edge of engine development and manufacturing would be hard pressed to run as many engine programmes at the same time as China is doing.
No PLA funded programme uses the WS13 or plans to anytime soon, so of course they are going to put it behind projects that they do use on operational and future planned assets in terms of allocation of critical resources, like funding; the most skilled and talented designers and engineers; supercomputer time; wind tunnel time and many other common shared goods and services.
Russia is happy to supply RDs to power JF17s, so there is just no pressing need to priorities the WS13 at all.
It might sound counter intuitive, but even be faster to put a pause on the WS13 development until work on the likes of the WS10 and WS15 has been successfully concluded.
That way, much like the JF17 programme itself, rather than spend time and resources breaking new ground, they could just piggyback on the work already completed and use off-the-shelf technology and parts to speed up development, reduce costs and risk, and potentially also boost performance.