Here, we are only talking about the main hero. Secondary heroes benefit from taking estates, literacy, and artillery. Water spells, when combined with earth and air magic, are usually left unused, so I don't take them. Resistance... there are more important skills, and there's no room for it. It makes sense to take it if there's a chance to acquire artifacts that grant magic resistance.
Tactics is certainly a skill with mixed results. Sometimes it helps a lot, and sometimes it's useless in every battle on the map.
What makes ballistics particularly good for Barbarians? To charge into a town with behemoths?
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