Is that useless?))
or
all Naga creatures gain a second attack for 3 turns.
Is that useless?))
or
when Necropolis units die, they drain a certain amount of health from all living enemy units on the battlefield, thereby resurrecting themselves.
Is that useless?)
+ all factions have slightly weaker abilities in addition to these ultimate abilities.
What is the point of having such abilities at all?
As for the economy, the main income always came from farming, so it doesn't depend much on the difficulty level, but more on skill and the map. However, the skills available in Heroes 6 provide good additional economic bonuses, and if there are a couple of experience stones nearby and the game is not intended to be a blitz, it is quite reasonable to spend some resources at the beginning on a couple of such supporting heroes.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!