J-10 is a lavy. J-11/15 are su-27 stolen designs. J-20 is coming from mig 1.44 that they probably bought. J-31 is a f-35 stolen design. They can't make their own from scratch.
Designing your own stuff from scratch carries enormous risk and also a specific set of skills. There will be Chinese designers designing their own planes and aircraft, but the fact that we have not seen their products just relates to their designs not working out to offer any benefits over existing foreign proven designs, while at the same time having an element of risk not present in proven reliable foreign designs that have had service and any problems already found and dealt with.
Eventually they will find western and Russian designs are not as suitable as a domestic design... the whole reason the Russians bought the Mistrals was because it was a ready proven design with most of the kinks sorted out and ready to make and put in service quickly... they would probably have four in service by now if politics didn't get in the way.
Instead they got an inside out look at a modern French designed helicopter carrier and now they are building their own designs presumably with modifications to suit their own needs better... I would guess distributed power systems so one missile hit wont take out both power plants, and probably some ice breaking capacity too... and I also suspect better armament.
Mig 1.44 is a project. The prototype didn't flew because they stoped the program but it didn't come from Stalin's ass. They developed it, engineered it and tested in wind tunels which is a huge part of the work.
The MiG did fly... there were reportedly two prototypes... 1.42 and 1.44... the latter was the flying prototype and the other was the stealth prototype which AFAIK has not been seen.
AFAIK they did fly the flying prototype of the 1.44, but it was cancelled and didn't fly very much... cannot find any real pictures of one in the air.
Problem of the soviet was that leaders obliged their companies to make analogues of every US project even if their scientists said it was dumb.
If US made a fighter with swept wings they would do it also. If they did a VTOL they would do it too. If they did 1 big aircraft and 1 small aircraft the soviet would do it too (f-15/f-16 - su-27/mig-29). They even made an analogue to the U2 plane.
Not strictly true, there was real competition in the Soviet Union... the west just never saw any of it.
For a replacement for the MiG-21 MiG tested swing wings and also lift jets to get the necessary small wing area for mach 2 flight but also to operate from airfield that were not 5km long. Germany was the first country to have aircraft with variable geometry wings, the adoption of swing wings for the Su-7 to create the Su-17 greatly improved the aircrafts performance, while the use of VG wings on the MiG-23 and Su-24 as well as the Tu-22M3 and Tu-160 made them very good platforms. The US used them for their F-14s and F-111s as well as their B-1Bs with the latter being their only swing wing aircraft still in use.
They had an analogue of the U-2 but not the criminal government that would overfly foreign airspace in violation of international law...
The US had no problem copying the MiG-25 to create their F-15...
They were throwing money on every dumb US idea. They lost too much cash and effort on useless project.
Yeah, the US didn't invent swing wing nor did they even come close to invention STOVL... everyone played at that and the Americas were the worst, they ended up buying British.