As for your "Politburo didn't intend" comment.... when was the last time you were involved in quality software development ?
Since the 1970s... continuously, embedded software for industrial use (= no bugs that any customer should discover).
Adding a feature like offline browsing takes more than a couple of lines of code.
Yes; it's called a "browser"
The basic issue is that IOS works hard to not expose what is normally called a "file system".
Yet, the file system is there, exposed perfectly well (to a degree supported by Apple) using widely used tools, with no jailbreaking involved.
Anyway, Atomic Web browser says it supports "Option to save webpages as HTML Only or Complete (Webarchive)" so I will give that a try
One has to go online first and let it grab the whole lot, which is OK.