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On random maps, warriors are undoubtedly much more practical. Mages need to replenish their mana to be combat-ready. Battle mages... what do they have to do with it? This is only relevant if you start as a Barbarian. Yes, they are better than ordinary mages from other castles, especially Dessa and Gandalf.
All the mage's advantages are nullified by just one or two artifacts – the Cloak of Negation or the Sphere of Inhibition. And resistance reduces them. But the warrior's advantages are passive; that is, they are always with him, and his army is strengthened by his parameters.
And most importantly, a mage casts a spell once per round, trying to compensate for the magical cast with what the warrior inflicts due to his skill advantage, which is not always possible. (Moreover, this attack can be reflected by resistance).
But! On maps where hit-and-run tactics are allowed, the value of a mage increases dramatically.
P.S. Why does everyone stereotypically think that only one strong hero should be used? Train 2-3 heroes with different functions. Then, where a mage is needed, there will be a mage, and where a warrior is needed, there will be a warrior. Through such skillful management, many strong players achieve a decisive advantage.