The segmented armour was used into the 3rd century AD, it was effective and its flimsiness is a bit exaggarated by some authors. If it had not been effective the Romans would not have used it for more than 200 years with constant improvements. There is still a quarrel about how far spread the segmented armour was. It was not used by every legion soldier and probably never by the auxilia. So lorica hamata, squamata and "segmentata" were used at the same time. In/after the near break down of the 3rd AD the segmented armour seemed to have disappeared.

If you are interested in such debates, http://www.romanarmy.com/rat/ would be a good address for example.

Btw the "segmentata" was not "the heavy Roman armour", being lighter as both mail and scale armour of the Romans.

Btw2: I hope EB will never be extended into the time of the Roman empire at the cost of the much more interesting earlier times. (beware: not discussible personal view contained in the last sentence)