I don't think Halone and Nophica *feud* per se. They are rivals because their traits are opposite but they don't necessarily hate each other.

Halone is a goddess of fury and ice. Nophica is a goddess of nurturing and abundance.

If you compare Ishgard and Gridania they are pretty opposite - frozen tundra vs large forests, rigid tiered society vs hunter/gatherers, constantly at war vs trying to exist in harmony. The city states here I think really embody the differences between their patrons. As you get more into the Heavensward story, keep an eye on how those trying to make peace with the dragons (a Nophican approach) are treated in Ishgard.