> what makes a mathematical assumption "natural" is how elegant or inelegant its consequences are

So now we start to argue about concepts that are not well defined in the context, introducing new terms, even?

Art for art's sake is just one aspect of science and craft. You might argue that mathematical knowledge as it is incorporated in the material world, e.g. in brains, books and soundwaves, has become a real matter which entails all the complexity that makes it so difficult to grasp.