This may not necessarily be the case. It all depends on how much you are willing to spend in RCS reduction measures. RCS depends on 3 major factors; size, reflectivity and directivity.Size, well it is not a large aircraft and hence will have a small RCS. Reflectivity is stealth shaping which is adequate on all 3 airframes, J-31, J-20 and PAKFA.However what you haven't considered at all is probably the most important of the three. This is what makes the F-22 the king of the hill while the others are only trying to catch up. This is Directivity or the materials that go into making the airframe and the radar absorbent materials including paints. F-35 uses a jacket made of carbon nanotubes and covered with RAM. PAKFA, currently unknown, what we have seen is only the outer shell. J-20 may be doing well with what it already has today.So, you see just looking at an airframe and claiming it is as stealthy as fully funded programs is not enough. As a matter of fact there is nobody on the planet who can claim the aircraft has this and this RCS just by eyeballing the airframe, especially if you are comparing two different airframes.The reason I came to this opinion of mine is not because of size or reflectivity. It is because of directivity. Considering SAC built the frame for export out of their own pocket, how much would they be able to spend on materials if aircraft like J-20, PAKFA and F-22 requirejust to get prototypes flying in the air. Sukhoi/Russia alone have been speculated to have spent $2Billion on the 3 PAKFA prototypes. Would SAC spend Billions for an export customer they may never get?Even getting JF-17 to fly cost $500Million, all that money on just an airframe, FCS and engine.This is an unpainted PAKFA, you have seen this many times,Unpainted F-35,Unpainted F-22,See how similar they all look. Now we don't know what goes below these paints, but we can guess these materials are not cheap.That's why this could be a bare bone aircraft with some loose ends. A PLAAF sponsored program may have a more stringent requirement in using materials compared to a pet project meant for export.As of today we cannot say whether SAC has been involved in a govt funded stealth program like CAC to claim they have been researching materials since sometime. All we know is they had a design as a competitor to J-20. There is no information if actual prototypes were built, like the YF-22 and YF-23 or whether they were flight tested. Perhaps it was a direct jump to the J-20 prototype after a paper competition. If SAC is able to use these expensive materials and built their own prototype after spending Billions all on their own funding, then be my guest, believe anything you want.It's primary role may be air superiority.Only if there is confirmation that it is a state funded project and not a company funded project.Your oldest J-10As will be old enough for replacement, nearing 20 years by the time J-31 or equivalent is ready. Your newest J-10Bs don't have to be replaced at the same time. As J-31s or equivalent's production continues the older J-10s will be subsequently replaced. Or are you suggesting the J-10As will receive service life extension programs to keep it relevant. Unless of course China is not able to manufacture the jets fast enough to replace older ones.