Start on "Hero".

Why specifically Genies and Titans? I believe the combat potential of mages is much greater than that of Genies, and certainly greater than that of Titans, because their numbers are always limited.

Titans turn out to be better in the long run, as they are more durable.
And everything is bought because there are no resources for anything else on a difficult map (I was considering exactly this scenario). And if the map turns out to be more or less favorable, everything is bought except for Rakshasas and Golems; they are saved for other weeks.

I usually only buy units of my own race, because what's the point of having, say, 9 Scouts and 3 Beasts? Besides, I desperately need money for my hero.

There is always plenty of money lying around on the map; I already wrote above where to get it. And without starting units, you won't be able to earn that money.

I almost always take gold for my hero, because there is never enough of it, and experience can still be gained in battles.

Not almost, but always.

Today, something like this happened: two Dragon Armors were lying 5 meters apart from each other :D
I thought the AI doesn't like attacking castles?

They attack when the danger is high. As a result, their entire army, which is twice as large, is defeated outside the castle.

I just played against the AI (one Elf) as my hero. I thought I would write something about it, and here is the second week of the Alliance, thanks to which, on a medium-sized map, I defeated him in the 3rd week.

In the first week, I got ore, wood, crystals, and gems (I didn't touch sulfur because I wasn't going for Mages, and the guard was inconvenient). Starting hero - Nurah, starting artifact - a bag of gold. In the first-second week, I captured the Golden Horseshoe, the Lion's Collar, the Dragon Tooth Crown, the Dragon's Tongue, the Dragon Leggings, the Flesh Tunic, the Emerald Slippers (sold), the Clover (sold), the Flame Rune (sold), and the Sword of Power (sold). The second hero was Orah, the third was Erling, and then there was a Dungeon on the map, where Ingvar was. Useful spells: Arrow, Regeneration.
I went for Summoning and quickly leveled up the Fire Warriors. If I summoned more than 30 Fire Warriors in battle, the opponent preferred to run away immediately)).
I got lucky with the week, but the AI would have lost anyway.