Chaos (Magic Depletion, Fire Wrath). Sorcery (Counterspell, especially against Necromancers, and Unstable Mana). Attack (Ranged Attack, Fire Arrows, and Cold Steel). Education (Scholar and Magical Reward with Graduate. Alternatively, you can take Magic Affinity. Then, don't invest in anything else in Education except for the main skill). And also, Mechanics. In total, this gives an additional 20% damage, which is very useful. Well, the rest is obvious. As an alternative, you can focus on magic. But I almost never do that. Maybe that's why I win?:) You can also buy it from the Artifact Merchant. In general, the Tower is the strongest Castle, and the Dwarves are also quite strong.

The Phoenix is very helpful, and the statement about the weakness of the mage army is incorrect. Without artifacts, their army is weak and cannot withstand any other army without the help of the Phoenix or other hero spells.

You say their army is weak? Have you considered that they don't need to go anywhere? And who do you think is weak there? The Titan or the Rakshasa? Or maybe the Djinn? Yes, you can attack a couple of units at once, for example, with Dragons, but they won't survive. The Academy has the strongest army, and I won't even mention the patched-up artifacts. Only the Archmages become a little weaker in a prolonged game.