I don't think approaching type systems from the mathematical angle is much help either. When I was learning Haskell, I started to try to learn category theory to develop a better understanding of what was going on. In the end I decided my time was better spent learning Haskell, and not category theory. Where they share words I look shallowly into the mathematical concept, but the understanding I develop is how it relates to me in a programming context. That doesn't mean I don't value that there is a mathematical basis for it though.