It’s good that China is doing everything in house. The technology developed for the WS-15, such as single crystal brisk blade for the engine, and other advancements can find their way into the WS-19.
Considering the infrastructure build to maintain the RD-93, it only makes sense to maximize the use of that until there is a substantial improvement to warrant the change; 20% increase in thrust when the WS-19 is ready.
I hypothesis on a light fighter was not about the Russians developing a light 5th Gen fighter, but a light 4 th Gen fighter at the same time the JF-17 came out. They win by having their engine in the JF-17. Down the line if the JF-17 keeps evolving into a Block 4 model, with a WS-19 engine, and some RCS reduction features, the Russians will lose out, but by then they will be moving on to market their Su-75 and will be leaving the light end of the market to planes like the JF-17. Perhaps their Klimov engine company will switch to making engines for loyal wingman UCAVs.