Some quotes from The Fall of the Roman Empire: A New History of Rome and the Barbarians, by Peter Heather.
“…this book will argue that the view that Rome’s own internal transformations had so weakened it by the fourth century that it was ready to collapse under its own weight in the fifth, has become unsustainable. The roots of fifth-century collapse must be sought elsewhere.” [pp. 14-15]
“‘What we call the fall of the Roman Empire was an imaginative experiment that got a little out of hand.’ You can only argue this, it seems to me, if you don’t let narrative history dirty your hands. Any attempt to reconstruct fifth-century events brings home just how violent the process was. In my view, it is impossible to escape the fact that the western Empire broke up because too many outside groups established themselves on its territories and expanded their holdings by warfare.” [p. 436]
“All the evils identified in the western system applied equally, if not more, to the eastern. If anything, the Roman east was more Christian, and more given to doctrinal argument. Also, it operated the same kind of governmental system over the same kind of economy. Yet the east survived, when the west fell. This alone makes it difficult to argue that there was something so inherently wrong with the late imperial system that it was bound to collapse under its own weight.” [pp. 443-444]
This reminded that I had seen a similar argument in Arther Ferrill’s The Fall of the Roman Empire: The Military Explanation. As I noted in my Amazon review of that book:
“There is a lot of nonsense in circulation about the Fall of the Western Empire. Ferrill gets past all of it by starting from one obvious but often neglected criterion: Any explanation of the Fall of the Western Roman Empire must also account for the survival of the Byzantine East.”