Definitely agree that the fall of the West is best understood as a consequence of the civil instability/war. I also think it is probable the successor states where most likely better managed/fruitful economically (although I probably would not say that to a Briton who had just been conquered by the Angles). Would seem to be a step too far to not give the Germans due credit for the fall of the West though.

The title Imperator in the days of the late republic was an honorific given to successful generals. This is is quite an apt title for the Roman political head during the Imperium. It was hard for the formally republican Romans of the early Empire to counter the precedent set by Julius and Augustus, who killed their way to the top. Normal stabilizing mechanisms like the divine right of kings were anaesthetized by Roman sensibilities. Conquerors did not face legitimacy issues like they might have in a political system with more ceremonial/spiritual backing.

But when the commander of forces on the Rhine was no longer a Roman General commanding Roman Legions but a German commanding his tribe that same process of conquering yourself a nice political office seems to have more political implications. Sure the Lombards kept the Senate but the lack of political union of the German tribes probably has something to do with break in political union of the Western Empire.