It's difficult.
If it wouldn't be - everyone and their mother would be making true all-aspect jets - by gathering knowledgeable people from forums, twitter, and youtube comment sections- instead of whole research institutes under the Russian Academy of Sciences. Yet this is just not the case.
Or, to be exact, it was the case with Qaher-313, but the result wasn't terribly impressive.
We can
assume the level they aimed at - by, for example, looking at how su-57 went for rounded EOTS&DIRCM domes instead of angular ones, or lack of toothing - i.e. measures that only have serious effect when return from everything else was already dealt with. We can assume that it isn't as high, but most certainly high enough to be tactically significant(otherwise - why bother?).
But saying more without at least a very good model is ... optimistic*.
Same is true for datalinks/data fusion and so on(but those are even harder to quantify, for obvious reasons).
The production quality of actual serial Su-57s changed
.
Finally, with all those details in mind, Su-57 has true stealth geometry, and was designed with a signature(s) requirement from day 1. Comparing it with hotspot treatment (F/A-18E, Eurocanards), or especially adjusting already existing airframe like F-15SE is ... disingenuous.
Thus, you're harsher on it than it deserves. All basic bits of information point to it being a competitive plane.
*We have
@Stealthflanker here, who actually does those models, btw.
On the other hand -
we have little to nothing on which levels FC-31 designers could have aimed at. It doesn't exactly take much to draw a basic stealthy airframe - the problem is the details. And on details...
We don't even know what the final result will look like. Things like RAM usage, edge treatment et cetera - on an (originally) self-funded(1), export
(2) platform, probably aimed at being affordable(3), created by a designer different from CAC(4)* - are a complete enigma. As mentioned in my exchange with Blitzo before - while we can criticize Russian EOTS balls - we don't even know if the actual FC-31 will use one, and how it will look. And so on.
*which is crucial, remembering the American A-12 debacle. But A-12 was at least designed for American use first and foremost.
Assuming that J-20A design had much higher(but how much?) goals for signature(s) is reasonable. Assuming the same for FC-31 - isn't.
虽然中文的确不是我的母语，我听过中方的意见。
But...
Per Piotr Butowski, Russian MIC has the exact same opinion of the Chinese defense industry, but in reverse; we actually had this discussion on sinodefense a couple of years ago.
While I personally find his estimates on this particular subject
doubtful - there is little reason to doubt that he actually has sources in Russia, and he is competent to write on what they think. Sources which few actual Russian experts may hope to match.
Thus, for simplicity's sake (and to try to avoid biases), I simply prefer avoiding "expert modifiers". Unless definitely proven - it's safer to assume both as equal. That doesn't mean they are - but, as with stealth, it is impossible to quantify.
The first FC-31 demonstrator flew back in 2012 - and the demonstrator, as different as it may be, needs to demonstrate something for the final aircraft. The difference with both T-50 and J-20 isn't big.
Thus it is a safe bet that its airframe design isn't all that much younger than either of those two. Yes, a more production-representative article flew only a few years later - but the same is also true for the other two aircraft.
Finally, the establishment of a promotion office may be a sign that SAC now thinks
they actually have something to market - i.e. FC-31 is close enough to a final form to sell it. It will place the whole timeline of the project even closer to Su-57 and J-20. Yes, a couple of years later - but it is younger, and had to make do with a much smaller fleet of test planes in the first place.
