I did not see the same linearity. Maybe he does consider Late Antiquity an improvement. I see things in terms of cycles anyway. Late Antiquity was the end of a cycle for a particular civilization. Do you consider Greek culture of the Archaic Period an improvement over Minoan culture and Indo-European culture that preceded it? Improvement or not depends on the criteria you set. Late Antiquity saw many disasters and spawned Christianity, so there’s some points against it.