Defences of the western Roman empire in 5th century

[Eleatic Guest]

My thoughts exactly. The difference between Roman 'factionalist' generals of the 4th century and the Germanic tribes of the 5th were that the Germanic leaders were driven by ethnic particularism. At their heart lie their tribe, not the Imperium.

That's not correct. The 'drive' of each leader, as far as we are even able to know it, differed from person to person and was also depending on time and occasion. Roman leaders were after as much power as possible - as early as the 3rd c. they did not mind all too much if they id not manage to rule all of the empire. And from the Terarchy onwards the concept of a partitioned empire had become acceptable as well.
Nor were they particularly 'tribal' compared to ('multicultural'?) Romans. Tribes were happy to mix and take on board everyone, tribesman or Roman.

And yet history proves the point that the Western Roman empire broke apart the moment foreign elements became so dominant that they couldn't neither be assimilated nor pacified by the indigenous Roman culture. And while Roman leaders were "after as much power as possible" for themselves, they also kept an eye on the integrity and interests of the whole of Roman empire. Otherwise rivals like Aetius and Bonifatius would have never saw a reason to cooperate so often and the Eastern Roman empire wouldn't have tried to support the weaker Western half for so long.

The difference between Roman warlords in the 4th and Germanic chieftains in the 5th century in terms of allegiance to the abstract notion of empire may have been gradual, but it was ultimately enough to make the difference between being and ceasing to exist for the Imperium Romanum. Being everything else equal, for the maintenance of the empire an Aetius (half Alan, but strong Roman affiliation) was always preferable over a Stilicho (half Roman, but IMO a bit less close to Roman culture) over a Geiseric (Roman hardly even de nomine).

You cannot upkeep a community in which people have no deeper interest into it than material gains, and Rome went down the drain the moment the people who carried its arms ceased to be identical with those who carried its culture. That is, despite all differentiation you correctly did, still the basic lesson to be learnt from the fall of Rome.