WS-13 is indeed ready but the problem is its maturity. The reason why the WS-10 is so mature/reliable now is because the Chinese have fielded them in their operational aircraft (i.e. J-11B) since 2009. The WS-10 in operation I'm sure helped the Chinese accelerate their improvement, esp with regard to the maturity of the engine. The problem is no such testing has occurred with the WS-13. Plus, the low priority of the WS-13 on the Chinese aeroengine agenda really does not help either. The WS-19 on the other hand has very high priority because it is meant to power China's medium stealth fighter (J-35) ... indeed it uses a lot of the same materials as the WS-15 and has roughly the same thrust to weight ratio of around 10.