Do you save the HTML, CSS, and Javascript, and hope that it works offline? I used to use the "Save page as..." tool back in the early 2000s, but it's become less and less useful, with too many dysfunctional disappointments.
No, I cut out some junk I don't need with the Printliminator [1] bookmarklet, then I do a *print-to-PDF.* This gives me a file. I can save the file, back it up to my NAS, search for it later, keep it with other files from a project where it was useful, and otherwise hang onto it. This is so common, in fact, that it's gone from being an obscure thing you could do with a Postscript-to-PDF converter or (before the adware/Ask toolbar scandal) the installing the CutePDF virtual printer. Modern OSes bundle a PDF printer, and print dialogs understand that you want to "Save as PDF". Google Docs and Office 365 editors allow downloading a document as a PDF.
I totally agree that a dynamic, interactive page or a comment section is not compatible with this model of usage. There's a lot of consumption of endless feeds, and a lot of one-time video views that also don't make sense to save as offline files. However, the web for creators, where people write articles that are worth hanging onto, has a definite place for PDFs.