Nice video, and I like Todd, though we disagree on a few things. I personally have found with my (fairly cheap, 175 lb draw) modern hunting crossbow, it shot through any kind of leather I tested it against, including some cuir boulli. None of it could stop the point of my Albion constable either.
Most of the tests I’ve seen online have shown similar results.
From what I’ve read, most “leather” armor used historically as armor (almost all of it outside of Europe) was actually buffalo hide or some other animal. In (what is today) India they used crocodile and hippo hide!
The most common actual leather armor I know of was cheaper grade lamellar in Central Asia, made of water-buffalo hide and often lacquered.
Generally leather in sufficient thickness to provide even marginal protection against real battlefield type weapons is quite heavy and stuff, and also fairly noisy. You might need say 8mm of leather for equivalent protection to 1mm of wrought iron (or the modern equivalent, ‘mild steel’). So you have to take that into consideration regarding weight and bulk. Leather of any kind was also not particularly cheap for settled areas unless you were in a cattle raising zone.
I think this is why textile armor was a much more common ‘poor mans’ armor.
It is also still debated whether the famous “Linothorax” may have included some cuir bouili