One thing I think the author doesn't flesh out enough is the impact of having the Germanic foederati who settled in the empire keeping their existing chieftan'

One thing I think the author doesn't flesh out enough is the impact of having the Germanic foederati who settled in the empire keeping their existing chieftan's rule. This helped create a parallel political structure that could easily fill in the void left by the crumbling Roman political structure, instead of having the Roman Empire split into mini-empires like the Gallic Empire in the 3rd century. Perhaps what might have happened without the parallel Germanic political order can be seen in the Italian city-states, although the history there is very specific so that's just what-if speculation.