Jokes are not to be explained usually, but well
Mythology does not go well with logic which is not unique to scandinavian one. By mythology, valkyries take the souls of fallen warriors to Valhalla in an effort to prepare for the final battle - ragnarok. New developers only added to this with their portal plot, it gives you the feeling of Asgard being threatened by superior forces, and the only thing the giants really need to win is a proper debuff (mistletoe) and a timely defence breach (portal). Recruiting human souls for the fight didn't help either, whoever came up with the idea of relying on them must be not very good at planning