Just checked the weight of my Sub by feel against my original MM and the Sub feels just a bit lighter.
I purchased the Sub as a back up and was expecting a similar sound to my MM, I surprised that it wasn’t, I use a fair bit of compression on the MM to give me a nice snappy sound, with exactly the same set up with the Sub it sounds horrible, it gives a distorted muffled sound, I had to reset all the EQ on my amp and zero compression to get somewhere near my preferred sound.
I would assume the Sub has cheaper electronics/pick up which is giving it a harsher gravely sound.