So there must be some A-2 brown lambskin bombers that are just as soft as the black lambskin MDR?
This is unnecessarily condescending. He's asking what would cause one leather to be softer, whether it's the tanning process, the thickness, the age of the animal, etc which is a totally valid question.
These are sorted, whether by Drew or at the market I don't know, to pull out all the shitty leathers - ones where the animal ran into barbed wire or had some other injury that would ruin the hide, etc. From what I've heard of the leather quality, these go beyond that to pick the really supple, thick leathers. Really top-tier leather houses like Hermes, etc will go even further and have almost zero variation between leathers but they charge a shit-ton for that and few here would or could pay the prices they charge.
On top of that I'd assume that the way they're dyed probably affects how they end up feeling, i.e. white leather is like painted on which is going to be a totally different thing than a rich brown leather.
Both of them are bombers?