Discussion of the Academy faction (Mages and Wizards). Tactics and their specific features.

In my opinion, the average game length implies some development of your army, followed by a rush into resource-rich areas and, likely, an encounter "in the center," where, as the saying goes, players of equal skill meet. I will base my reasoning on this.

but in the endgame, Nura's ability is practically useless.

I believe this is a very common and dangerous misconception. An active playstyle for a mage involves constant and repeated spellcasting in battle; otherwise, either the monsters are too weak for the game, or you will hopelessly fall behind in development. Very often, by maintaining the right pace, you encounter an enemy with no mana, which is almost a guaranteed death against powerful units, and the Dark Elf mage almost always has full mana. How many games in all the installments have been lost because the enemy caught you with no mana (difficult battles, no spellbook, didn't reach the mana well, etc.)? Nura's special ability not only allows you to fight more often, more actively, and more effectively but also ensures that you are always ready for battle.

I prefer to lose 10 gargoyles while clearing neutral creatures.

Maybe I'm not playing the Hive correctly, but I have the impression that the difference is not just a few gargoyles, but in the levels of monsters that can be cleared without making loops.

I also wanted to ask for your opinion on the "Elemental Balance" perk: is it worth taking against necromancers? The likely opponent is Vlad.

Against Vlad, it's definitely worth it. He can't switch to another magic school, and he can't take Elemental Balance. The rest will be finished off by his Summon and Archer under the Sign. I believe that in most of these scenarios, Vlad is doomed.
However, if your opponent breaks away from the stereotypes of version 1.0 and takes Zoltan, that will be a problem. He may not only have Elemental Balance but also Darkness with Plague and Matyuk, and even Chaos (not all at once, of course). Considering Education and Attraction, his stats and mana will be in good shape, and he will also ban your Archer and any other low-level damage dealer you have. And he will start using his considerable Sorcery to its full extent, and his Defense parameter will also be decent. Here, you need to find a way out by taking several Chaos spells, building a Guild, and developing your army, which is not always possible to do simultaneously. If there is nothing to cast, almost all of the mage's primary parameters are useless, as is the Sorcery skill. It is not for nothing that Zoltan's biography explicitly states that he is an antimage.