Well, if you are using magic to cast a hex, then chances are that you *are* doing something obvious, or taking time to do it, or another requirement for use magic.
More importantly, they have a different style. Balancing pure mechanical effectiveness was not my primary consideration when I wrote the moves. How it affects the fiction you generate in play and what a move implies about the hunter who uses it are just as important.
So:
- Hex implies you are a magician who specialises in hurting others
- Big Whammy implies you lash out with magic as easily as with your fists or guns.
(These are not be the only things they imply, of course).