yes..thats because china spectacularly failed to build a jet engine despite tall claims of being a technological giant...
There are too many projects going on in China, China needs to priorities and we did it by concentrating on WS-10 which we succeed. WS-13 is a second tier project.
well you dont semd a chase plane which may fall off the sky or malfunction amidst a multimillion dollar experiment..Plus the plane is versitile and compatible with all the new pods chinese want to fit to it..
Chinese cant do that to their sukhoius...can they?
In addition to all that..there is no friendship for the hell of it in international politics..Countries dont spend their resources and money just on friendship thre is always a gain to be made..
If you think your rulers are stupid and blindly spending millions on Pakistan without any gain to be made...?
You shall be grateful for that help instead of doubting it. But China is also grateful of PAF letting our test pilot Lei Qiang to flow PAF F-16. It indeeds help the J-10 project at a time when China is really weak in its military industries in the early 90s.