I think I need to clarify, as I didn't really say that much about it when I first posted the Dahomey image.
Firstly, I am assuming it to be authentic, but so is the one with them fully covered. So no, I'm not going to claim that they went into battle in the more-revealing outfit. However, the crowd scenes also could include artistic licence in covering up those parts deemed offensive to a Victorian audience. Prejudice against female bodies has been around for a long time.
Secondly, I don't think it resembles the Elven Women outfit. It's presented as an alternative rather than as an example.
But what I do think is that the tops they're wearing in the engraving(?) that I posted, and in the one that 227 posted, are valid and practical clothing for women warriors, just as practical as the fully-covered version that Guy showed. If anything, it's more practical because that cross-over can be used to stash knives, food, the baby, whatever.
And, as Guy mentioned, this was a genuine army who successfully fought against opponents who had heavier fire-power, without using armour.
The only practical argument that I can see against dressing the Elven Women like this is the climate difference, so I will give you that. We do have cold-climate precedents like the Berserkers, but there's a big difference between stripping off while going into battle and stripping off while hanging around your camp, so it doesn't help my case much as an example.
Given the number of real-life examples of tribal warriors, freedom fighters, rebels and whatever who fought wearing no padding and no armour, this could equally be expressed as a criticism of the way that the male elves dress. Their usual tactic is guerilla warfare - they attack out of ambush, they depend on mobility and in being able to sneak and hide, and now that they're about to fight an army they're going to have problems, because they're probably NOT in a position to re-outfit.
Iorveth being over-dressed and over-padded for this environment can be justified - as their leader he has to be able to stand on tree-trunks and give defiant messages without worrying about sneaky crossbow bolts. But for the rest, freedom of movement has value, and NOT wearing armour makes damn sure that they learn quickly to stay hidden. (Similar to Zivik's argument against protective amulets).