I think the idea is to have you go through different play styles before you become a "legend" worthy of Valhalla.
Narratively it makes sense. You start with brute force then become more refined in basic warfare, once you've mastered that (as demonstrated by you taking down the plains boss) you start to learn the mystic arts. You start to become more than just another warrior.

I imagine we'll eventually produce equipment that combines the two disciplines.
For example, Thor's hammer (just a random example) is a weapon of war *and* a focus for magical energies. It would require mastery of both combat and magic to wield effectively.
Only someone who had done that could defeat Odin. Which is likely whats coming.