Light Infantry vs Line Infantry

[Didz]

Obviously skirmishing was done in loose order and therefore relied upon experienced men who could function thusly without routing or deserting.

Exactly my point. Skirmishing is always done in loose order, therefore it is a nonesense to have units with the ability to skirmish who are not deployed in loose order, as it renders them useless.

In fact, historically the evolution was the other way round. Early warfare was always conducted in loose formation, not just because men were not trained to fight in close order but quite simply because men could not fight in close order using the early weapons available to them. They needed space around themselves to fight and so they fought in loose formations. The development of drills and weapons that enable men to fight in close formation was a technical evolution that included the Greek Phalanx and the Roman Legion as its most famous exponents.

You do not need to train a man to fight in a loose formation any warrior will do that naturally, you only need to train a man to fight as part of tight unified group.