If you watched the video conversation between Jonathan Rowson and me (thanks for mentioning it!), or read my article in the Sideview that prompted Jonathan to invite me to his channel (https://thesideview.co/journal/what-is-metamodernism-and-why-does-it-matter/), you know that I'm not convinced that the metamodernism described by the Hanzi authors is at all the same as the academic-originating metamodernism described by Vermeulen and van den Akker, and many others including myself and my writing partner Linda Ceriello. One really important difference is that the folks in my "camp" really mean it when we say we're talking specifically about an oscillation between modernist and postmodern polarities, NOT oscillations between any sets of opposing positions (chocolate vs. vanilla, vegetarian vs. hunting, Democrat vs. Republican, Labor vs. Tory, etc.).
The general approach to thinking characterized by oscillating/integrating/embracing seemingly opposed positions could be called multi-perspectivalism, and I would say that THAT is a postmodern thing.
The descriptive vs. normative (prescriptive) dichotomy is a way that people who use "metamodernism" in the general way that the Hanzi authors do attempt to account for the existence of the earlier and academically much more firmly established metamodernism of Vermeulen, van den Akker, and others. At times I have used those labels myself, out of convenience. However, I think it's an inadequate way to make the distinction, for two reasons.
1) There is an actual difference in content. The sensibility or structure of feeling that we've observed in cultural products prevailing in the period beginning shortly before 2000 is not the same sensibility promoted by the Hanzi authors and those inspired by them.
2) While what my "camp" does is primarily description, and what "they" do is primarily prescription, we both also do some of the other. I have heard Gortz attempt to give examples of existing cultural products that fit his definition of metamodernism. And, as you pointed out, we academics and journalists who do the "cultural" metamodernism do end up championing or celebrating these products more often than not.
I should note, however, that the lens of what you call "descriptive" metamodernism HAS been applied critically to things that the observers don't like. And I would like to see more of that.
This may or may not be a fair critique of your critique, but from my point of view, what you've largely done is offered a reasonable criticism of the "normative" (I'm just using your distinction for convenience) "metamodernists" while erroneously conflating that body of thought with the work of the theorists of "descriptive" metamodernism, seemingly largely gathering your sense of "descriptive" metamodernism FROM the point of view of the "normatives," who I don't think entirely understand "descriptive" metamodernism.
