A self-ping for a morning comment. I think your list is a good one. I’d add a couple - first, the shift in political emphasis, military resources, and especially revenues toward Constantinople after the split of the Empire, and second, as Gibbon proposed, the dramatic shift in talent from the secular government to the building of the Church. It’s a little difficult to understand just how radical a shift it was until you consider that Christianity had, in the same period, run like wildfire through the Goths, and that the very men taking over the Western Empire in 476 AD were Arian Christians. The notion of a barbarian taking over the monarchy was tempered by the realization that the barbarian was a Christian, not to mention the leader of an army that was as close to Roman as anything in the field at the time. The Emperor was, by then, in Ravenna anyway, not Rome. It may not have been as jarring a change as it might appear to us at this historical distance. IMHO, of course.
The truth is, the Roman Empire did not fall in a day in 476 A.D., it withered away until nothing was left but a shriveled denuded trunk of its’ former self.
Then the Goths took over, then the Byzantines sought to recapture the Italian peninsula in the 6th century.
The Goth & Byzantine wars devastated Italy.
That was the onset of the Dark Ages.
Never mind.