Spartan army 400 - 390

[Giannis K. Hoplite]

Heroic nudity seems to me a valid concept, but heroic tunic-wearing is less likely

Doesn't this mean that heroic nudity is also not so likely as well? What makes it unlikely? The nudity? If it was this,then why all those statuettes and vases with fully armed early hoplites with bell cuirasses,greaves,thigh and arm guards but NO chiton?

I don't believe that armor came and went away at any point,at least not as a fashion nor as an intentional lightness of armor. In all ancient societies there were a percentage with armor and one with less or not at all. What were the factors that made the Greeks abandon and then again re-equip themselves with even more armor than before?
There is also the possibility that the hoplites had the necessary armor and they used some parts of it or all of it according to the situation. For example in the late 5th century both Athenian and their allies and Laconian and Peloponnesian troops were used in naval battles,night asoults and ordinary phalanx battles. I'm sure if the passengers of a trirreme were ordered to form the phalanx and march in an enemy territory 2 kms from the coast,they were better armored than when they were disembarked in a small beach from were they would asoult a small enemy castle some dark night and return back on the ships.
Thucydides gives many times indication of body armor talking about "thorakes",even when the Plataeans asoulted the Spartan wall!
As for helmets, the later chalkidean helmets,for instance,did not provide less protection than the earlier Illyrian,nor the early chalkidean of the late sixth-early fifth century bc.
In my opinion the key is that hoplites took much different responsibilities from the Peloponnesian wars and afterwards. The Spartans in Sphacteria were ship passengers. The fact they wore pilos cap doesn't mean they always wore this type of helmet. Given that most young men during the Peloponnesian war took part in irregular skirmishing rather than hoplite battles,and many times served also as rowers as well as passengers(there are such instances mentioned),it is logical that most gravestones depict lightly armed men.
The problem is we don't know the percentage of armed men in a phalanx for any given period. How can we say they abandoned armor?
Khairete
Giannis