Power Buildings

With the Nomads, there's also the useless caravan.
By the way, Nomads lose to Harpies even in terms of movement range on the map, so building them isn't very useful.
The Arena isn't that necessary, in my opinion. +10% to resistance is more appealing if you have extra money.

The difference in movement range on the map, 27 versus 28, isn't critical (Cyclops and Behemoths have only 21). But the resistance issue is interesting. On AG.ru, there's a formula for calculating resistance, and everything is explained well. So, I won't go into details, but I'll just say that 1 Suppressor will only give 10% to a hero without resistance. For a Barbarian with his initial 30% resistance, the Suppressor will only add 7%. And 10 Suppressors will add only 65% to the hero, and even less to the Barbarian - 45%. Furthermore, the Suppressor doesn't require personal acquaintance with the heroes and is more useful in the later stages of the game when you start encountering various mages. Also, increasing attack/defense by 20-30% when leaving the city is also good for a fighter, especially since once he goes on a raid to that city, he won't return (and won't receive the bonus later). Besides, both upgrades are required for building certain monsters, but the Suppressor is twice as expensive and isn't a mandatory building. So, it's worth considering.