First off, gore-tex is shit. But, yes, leather is nearly as non-breathable as a plastic bag that's why the traditional use of it is for things like elbow and knee patches, extreme heat protection, such things. Boots, of course. The solution is as always proper layering, not exactly a modern invention: You wear something breathable for warmth, and something non-breathable that you can take off, and has breathing flaps (rain doesn't fall from below), for water protection.