We view Arms as a soldier, like a career military infantryman. Think Gladiator. We view Fury as the wild berserker from up in the hills. Think Braveheart or Conan. It's easy to argue that bleeds or mobility fit one or the other depending on your point of view. Arms feels tactical (in the sense of having an answer for various situations) and Fury feels reckless. The Arms warrior has pet names for all his weapons, while the Fury warrior shows up for battle drunk and half clothed.