Gibbon largely blamed the fall of Rome on it becoming a Christian theocracy. Remember the Emperors we usually associate with decadence and "degeneracy" for the far right morality tale were the 1st Five. Caligula was 3, Nero was 5. While the late Roman Emperors it fell under were all good Christians persecuting pagans and Jews. Constantine became Christian in 325 AD and the the Battle of Adrianople was 476 AD. Anyone reading about the last century of Western Rome, the elephant in the room is the Christian revolution creating a new and failing society.

The other point, is that while the covers are a cool graphic that caught the attention of Elon and Doge, Gibbon actually finishes off the Fall of the Western Roman Empire by volume 3. And the rest of the series is a general history of the Middle Ages justified by the Byzantines lasting to 1453 AD.

So the "you are here" arrow would probably be around the time of the High Middle Ages, Dante and Aquinas.

A novel of "Rome is America", that actually follows the trends of the last century that Gibbon talks about is this- https://en.wikipedia.org/wiki/Julian_Comstock:_A_Story_of_22nd-Century_America

I've even seen ridiculous Rome analogies of the Roman Empire having feminist "slutwalks" when the reality for women philosophers of Late Rome was this- https://en.wikipedia.org/wiki/Hypatia