You summarized already in your sentences ("I'm bewildered by this article. It seems really damaging, and like it doesn't really add very much to the corpus they've already published") how you feel and why you feel that way: it
appears damaging because it contains the paragraphs that explicitly contain the words "it's damaging." But it's just a general introduction to the "juicy bits" without the bits themselves.
In fact you recognized this too writing: "it doesn't really add very much to the corpus they've already published." Once you attempt to identify the new information, you can recognize that 99.5% of it appeared in some other form before.
The older published documents already were marked "top secret." This markings are given to the content that is considered "damaging" by these who write the documents. You just percieved it differently because these markings were just markings for you, not the sentences spelling out "damaging."
Still, the value to the public of this very document is that it's a single document summarizing nicely the previously disclosed ones in much less words. By its nature though it doesn't contain the details published previously. (Edit: technically, it's a set of the documents but all of them together appear to me just as a big table of contents for the disclosures already published.)
Now let's discuss the new 0.5% of information, even if it's very general.