When did the Roman Empire fall (your thoughts)?

[Robert Vermaat]

I thought Hugh Elton had disproven the idea that the late Roman army was mostly composed of 'barbarians.'

I have Warfare in Roman Europe and while Elton may be right that the regular Roman army wasn't barbarized it still seems to have practically disappeared even prior to the loss of African revenue in 439. Aetius had to hire Huns, evidently because the regular forces no longer amounted to much. Not too many citizens wanted to serve anymore...

I don't see why Aetius hiring Huns 'evidently' means the regular forces no longer amounted to much. For one, Aetius had a special relation with the Huns and seems to have used this to aquire a personal army (which gave him political power). Such personal armies are new for the 5th century, Stilicho may have started the practise.
But even if not, Germanic forces and other non-Roman troops had been hired even during the time of Roman conquests. Ceasar used Germans in Gaul and in Britain - surely no sign that his legions did no longer 'amount to much'?!
Constantine hired tens of thousands of barbarians in his civil war against Licinius - such troops were hired to get numbers, they do not tell us anything about the quality of the Roman forces.