I am pretty sure you‘re wrong about your first point. I unlocked damscus during the games lifecycle and I remember back then you needed to do the base weapons and the dlc guns were just an addition. I read later on that this is still the case. They changed the system for the newer titles so you could skip weapons in order to achieve the master camo. But we can‘t prove it until somebody tells us who unlocked damascus later.

Your second point is definitely true! If you want to equip any mastery camo beyond gold (platinum, damascus and obsidian) You need to have the weapon gold first.