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Against such a Barbarian, you have warriors in your army (Titans, for example). You cast Accuracy on the Titans and... :)
On small maps, you won't be able to develop Titans: "Island of Marantea," for example. And on large maps, 3 Barbarian heroes at level 50+, you can't scare them much with Titans. They move first because they are very fast, have very good defense (150+), their attack is not inferior, and they have magic resistance (100% + artifacts for defense, like Chaos Armor, etc.).
In general, tactics are great; what's wrong with them compared to spells? Nothing, even better.
A skilled tactician who knows Nature Magic (Mass Speed) or Chaos Magic (Mass Haste) + Mass First Strike or Mass Sneak Strike – that's power.
1) With good speed (which is very important for a tactician), he moves first.
2) Cast a speed spell.
3) Speed spell + tactics = the creature moves almost across the entire map, or even the whole map. It depends on the creature. (Champions, for example, will reach the first ranks, even if they are all standing in a pile. Imagine the damage.)
4) Attack and defense skills: 10 Archangels chop up 10 Black Dragons, completely without losses (without resurrection).
5) And for dessert, leadership: +5/+5 morale/luck.
And you keep talking about magic...