Another primary consideration in introduction & eventual disappearance of Segmentata?

[Nathan Ross]

I never implied that the Antonine Plague was Bubonic

That was a reference to your point above: "Disease, probably more than any other factor, brought the Romans to their knees... they were hit by both Smallpox and the Bubonic Plague". Were you referring to the plague of Justinian for the second one?

there is no reason to suggest that even the mighty Western Roman Empire was able to weather the near simultaneous weakening by the plague, and the Great Migration that occurred before it was able to return to its power. 

But it did weather the plague. The west did not fall for over two hundred years. The migrations were in the late 4th-5th centuries, so were not 'near simultaneous'. There were plague outbreaks after the Antonine one, and doubtless they contributed to imperial decline, but your original point concerned the second century.

The East was much stronger economically and was able to weather the storm of the 5th Century.  The Western Roman Empire was not.

That seems fairly uncontroversial! But, again, you're talking about the 5th century here.