China's landed on the more optimistic parts of the spectrum. I would like the "realists" to take a tally of their predictions over the years and honestly examine how things have turned out. Far more often than not, the more "optimistic" predictions turned out correct, and a good part of the times they haven't been correct was because of them not being optimistic enough. Would the "realists" have predicted the present J-20 production rates five years ago? Or that the WS-15 would enter service before the Izd 30?
To be fair, it's not a constant parade of Ws. I would have expected some activity or even a first flight of the H-20 by now, which means the program is having difficulties or it's being reconsidered, neither of which bode well.
I would actually say the optimists track record is not particularly great, especially for engines.
For WS-15, being ahead of Izd30 is not a reflection of WS-15 being particularly successful or quick but rather Izd30 being slow.
Since the early 2010s, the idea of WS-15 entering service was constantly thought of as "just around the corner" or 4-5 years away by many optimists. Finally it seems like predictions of that nature from 2020 might be bearing fruit.
Similarly, predictions of H-20 as you noticed, as well as for the Chinese carrier fleet size by 2030, have all been somewhat behind as well.
All of the above have good reasons why things didn't pan out the way they did from both procurement and strategic perspectives when looking back in retrospect.
However the examples you have listed where things became more "successful" than previously expected is exactly why PLA watching as a method tends to have a good track record -- namely we do not try to boost and exaggerated and overreach, so that there does not tend to be walk backs of overambitious claims.
When new credible rumours indicate that a revision of a prior, more conservative prediction can be expanded or made more ambitious, then that is the system working as intended.
But getting high off one's own supply is something that the PLA watching community in English, has by and large been okay at avoiding most of the time, and it would be beneficial to continue it that way.