The radar and RCS argument assumes the J-16 would have had a difficult time with the J-10C RCS which if true, would be seriously disappointing. The J-10C isn't stealthy in the least, especially with air to air missiles. Let's say all the equivalent levels of technologies are present, the J-16 may detect the J-10C slightly later but even PL-15s launched from the J-10C will be obvious enough to the flanker pilot who will have huge missile and fuel advantages. J-16 can carry 10 MRAAMs? I think the J-10C is at 6? Then the massive fuel advantage of the flanker. Fourth gen BVR between similar EW, ECM, avionics platforms are attrition which the J-16 should win overall if enough simulated engagements are played out. RCS and radar ability difference MUST therefore be the reason behind this surprise (to me at least) and that is surprising!
I find it hard to believe J-10C has whatever EW cloaking magic that somehow PLAAF isn't putting on a more expensive fighter with considerably more engine power and onboard space.
I'm not suggesting that J-16 would have had a "difficult time" with the J-10C RCS, but more that the overall balance of each side's RCS, weapons loadout, active sensors and EW and ESM may have been enough to put both aircraft on an even footing.
I.e.: for one, I don't think a J-16 is necessarily significantly inherently superior to J-10C in BVR assuming a similar engagement profile for each side and similar fuel loads etc -- of course, having those "engagement parameters" be equal for a series of DACT engagements makes sense, but for system of systems warfare those parameters may not be useful or reliable and larger theater level exercises like Red Sword would probably alter those parameters to be suitably more realistic.
When you introduce force multipliers and other confounding factors then the effective net combat potential of each platform will likely differ -- if we take a very simple hypothetical e.g.: four J-16s + AEW&C vs four J-10C + AEW&C --- I would say that the effective net combat potential will likely slide meaningfully towards to the J-16s, because each J-16 carries more A2A missile than each equivalent J-10C, and each side's AEW&C will likely largely cancel out any differences in RCS between the individual fighter platforms, and also because the J-16's significantly greater endurance means they can maneuvre to defeat incoming missiles and then re-engage as well with greater freedom than a J-10C that has ejected its fuel tanks.
But even the addition of a mere AEW&C significantly changes the way that a four ship formation of each aircraft may have their combat capability enhanced or depleted, and in a real conflict with more confounding factors, the strengths and weaknesses of each aircraft type will also be further altered depending on the environment.
And I also repeat, we don't know how close the margin of victory/defeat was. I would be surprised if J-10C completely dominated J-16 -- but I wouldn't be surprised if J-10C managed to eke out a small but notable margin of victory because I think the strengths and weaknesses of J-10C and J-16 on a fighter platform vs fighter platform comparison (i.e.: not system of systems warfare) are largely equal for the kind of tactical DACT type exercises that Golden Helmet is thought to be.
Putting it another way, on an individual fighter platform vs individual fighter platform kind of engagement or a limited multi ship vs multi ship type engagement, I don't think either J-16 or J-10C has any inherent overwhelming advantages or disadvantages versus one or the other.
But that isn't to say that they do not have advantages and disadvantages at more complex system of system environments.