WS-13 is a low priority project. The immediate end user is Pakistan and the uncomfirm J-31. Therefore it do not take an expert to figure out most resources are not pour into it. Then you need to remember WS-15 which is an important project that will also take away significant amount of talent and resources. Why would I be suprised if WS-13 has many issues despite being in the same generation of WS-10A? Definitely, the lacking of talent and resources due to low priority has result in the slow progress.
Not quite. What about china´s UCAV programs? already they had to strap a RD-93 engine on Sharp sword UCAV. China needs an engine in that thrust range, otherwise all UCAVs will have to be propelled by russian engines.