Was J-8PP ever operational for the PLAAF? I don't think so. Is it reasonable to derive the performance of this jet for its variant's documentation? Maybe. Is the J-8PP completely unbased? I disagree. I think the project is a mix of uncertainty, educated (hopefully sufficient) trials, and excitement of finally modelling a classic yet mysterious airframe in full fidelity. People simply shouldn't label it as "True or False", but rather a module that has required more technical compromises than the existing ones due to its complex background.
I totally get your point of raising the concern, and I agree with most of your arguments. But it's the way you presented your conclusions that outraged people, because nobody wants to see their hardwork / dedication / love to be labelled as "fake". Yes, I wish they could do a full-fidelity model of a variant that actually entered service, but I am more glad that we could even receive a compromised model verus none. I like your argument of using the F-20 Tigershark example, but what if the base F-5 doesn't exist and is impossible to implement, would the community still reacted the same way? F-20 would be more of a cherry on the top for the fans, yet a standard J-8 is something cannot be modelled at least within the next 15 years.
I personally don't think it lowers the DCS standard, especially if Deka and ED determined that there is enough documentation to start the project, but it is in the end less ideal. And like everyone else says, if you don't like it don't play it, but please also be friendly to those who cherish it.