I'm not sure if that explanation makes sense for a few reasons:

1) It seems like a contradiction to say that if there is an advantage in armor that is lost when equally armored, does it in follow that giving up the armor advantage gives you an advantage?
2) If you reduce armor to move around, wouldn't that give defenders a huge advantage?
3) And while battles happened all over the place, usually there were only one or two battles (related) in a given theatre each year because war was expensive and the fighting season was restricted by planting and harvesting times (unless you were Sparta or you paid your troops like Athens did in the later 400's BCE)

Does anyone have some good books on the subject that specifically details the Peloponnessian War? I've already looked at the Osprey 480-323 BC Hoplite book, Storm of Spears and am currently reading Land Battles in 5th Century BC Greece: A History and Analysis of 173 Engagements to try and get a better picture of how battles were fought during this period.