The spiritual trait gives free potency to disciple units, and paladins are disciple units. I've seen disciples (tier 2) gain passive xp from potency, and I've seen priests (tier 3) gain passive xp, both with and without potency. But I've never seen a paladin (tier 4) gain passive xp, either with or without potency. I assume that this is working as intended, and the spiritual trait is pretty powerful regardless, but could someone explain the design reasoning here to me?