The phenomenon Adams is talking about here is largely a post-WW1 phenomenon in UK culture, related to the post-WW1 malaise. His best examples are post-WW1 (Paul Pennyfeather, Tony Last, and the book by Stephen Pile). The others arguably don't really fit (e.g., the core delight in Gulliver is the reader thinking they are smarter than Gulliver; the reader doesn't identify with him). It's not exactly a new observation... one of the motivations both Tolkien and CS Lewis had for strong characters like Aragorn was to present examples falling outside this cultural drift.

Yes. See also Fleming’s James Bond. Dickens’ Nicholas Nickleby. *

This phenomenon is post-WWI and post-WWII and losing the greatest empire in history in a single generation trauma being retconned as if were the historical English perspective.

* Removed previously incorrect statement including Edgar Rice Burroughs who is an American although Tarzan is English