Despite there being Nintendo Hard quests, most of the party, except maybe for Iu, aren't really that useful. They don't really train their abilities and mostly just stick to the sidelines. While you could say that they can't gain XP out of combat, training still has an effect, like when they did sword training with Captain Cahvell. And while the early Wind and Fire magic are not that great at early levels, Iu has at times shown that Wind magic is effective at higher levels. But we never see Yuka use it after the first time, or even attempt to see what the higher levels can do. Even at the lower level, her fire magic is still effective, it just turns her staff into a red-hot poker, which could work in melee.
