Antonio Santosuosso, in his book (which I have not read, but will be looking at today), Storming the Heavens, claims that ethnic Italian troops made up 65% of the army under Augustus, 49% under Nero, and only 10% under Hadrian. If true, the barbarization of the army had begun quite early. If these numbers are accurate, I wonder if the problem lie not with the composition of barbarian or non-italian troops, but the establishment of non-mobile field armies stationed in certain portions of the Empire, and such decrees that created the Numeri and the Annonae Foederaticae? While there is most likely more examples, these both seemed to add to the non-integration or romanization of "barbarian" troops, and would make it much easier for a man like Arbogast, Stilicho, or Ricimer to rise up and take advantage.