When did the Roman Army decline?

[Mrbsct]

So Gratian and Theodosis decided not crush the Goths after Adrianople purely due to political reasons not military and manpower issues? The manpower issues started after Constantine's tax law and religious reforms if anything.

I don't understand how the Limitanei are somehow "good". Julian seemed not to even rely on them in Gaul. There is a reason why by the time of Strasbourg, commanders were very conservative not to sacrifice their precious Comiatenses.