Anyone know what this argument is about?

[Anomalocaris]

One could argue that the Comitatensis and limitanei system worked reasonably well until Adrianople. Between 50 - 31 BC the Rome seems to me to have readily made up several times the loss at Adrianople. It seems to me what doomed western empire after 376 was the inability to make good losses in a way that she might have in second punic war or civil wars of 1st century BC. Apparently roman empire of the 4th century is not able to truly mobilize manpower reserve into deployable armies the way it could during the 1st century BC. Since the total manpower pool in 4 th century AD can't be less than the pool of citizens before 1AD, I think some sort of societal transformation, possibly tied to christianization, possibly not, must underly the decreased martial vigor of the empire.