Maybe instead, we could create a spell that removes a portion of the movement penalty for traversing difficult terrain? This could be stacked with "pathfinding." I'm not sure about its usefulness, but it fits the lore perfectly: swamps and snow can't stop a water mage. As a result, with maximum water affinity and maximum pathfinding, the penalty could be completely removed or even turned into a bonus, which would result in an interesting mechanic where roads are unnecessary for a water-aligned hero, or even slightly hinder their movement speed.