As I suspected, angelo hasn't even read the book he's claiming to cite. Also, if he actually knew anything about it, he would know that most scholars consider the Decline and Fall of the Roman Empire to be mediocre history. Its influence is mostly from its style; it established the benchmark of English scholastic writing, the so-called 'official style.' As such, it is a much imitated book in its cadence, choice of words, and dignified exposition. As history, it makes a fine beginner book, detailed, easy to read, relatively non controversial, and not particularly insightful.
I suspect that if angelo had actually read it, he would be able to write better himself, as this is the primary value of the book.