Another primary consideration in introduction & eventual disappearance of Segmentata?

[Nathan Ross]

It was after this, the beginning of the 4th century, that segmentata started to be phased out

Aha! A controversial view, but not without supporters (see the recent Ross Cowan 'legionary' book, for example!)

I tend to think it had been largely phased out by around the mid 3rd century, but lingered in use in some areas.

However, as we know from the Leon finds, our views in these things can easily be overturned...