> of the 8000ish english in the battle of Agincourt some 1 to 2 thousand wore heavy armour,

Part of the issue here is that the English fielded significant amounts of longbowmen as light infantry, as English doctrine of the time focused on heavy use of archers for ranged supremacy, contrast this with the French who were reverse in proportion and fielded primarily heavy cavalry/infantry (men-at-arms and knights dismounting to fight on foot for tactical reasons) with small numbers of lightly armoured specialists such as crossbowmen, cannoneers or pavisers.

It is also worth noting, that this is the point in western Europe where large scale manufacturing starts bringing down costs and that even common infantry were becoming better armoured than just a helmet and aketon.