I fully agree with the first statement. By 400 A.D. the Roman Empire was in steep decline. The previous "Pax Romana" era meant no more major wars and the military got soft. A larger proportion of the army were from outside the Roman core, the Empire being stretched over most all of Europe, losing border security, and the lack of a major enemy allowed hostilities to be turned inward.The Roman's that Atilla and his men defeated were a pail comparisson to the armies that marched with Scipio or Caesar, the Huns were not the partheans.
Alexander would have crushed Atilla.