The other thing to keep in mind, is that in comparison to steel or iron armor, leather thick enough to protect you from being bruised by even a rataan stick ala SCA combat, it not exactly light.
A real historical rivated mail shirt which can actually stop sword cuts and arrows weighs around 12 - 15 lbs and is flexible. A leather cuirass by contrast, hardened or otherwise, thick enough to (maybe) stop a sword cut weighs probably quite a bit more than that and will be very stiff and cumbersome. And fairly expensive.
The idea of leather armor as 'light' and 'flexible' and cheap alternative to metal armor is born of a whole host of cliches and mistakes that keep getting repeated around and around in circles. It's up to us to kind of correct that! :)
G