I played a few duels, and the uselessness of the Destruction school became apparent, both in specific cases and on a global scale.
For example, in a match between Ibba (Dwarves) and Dugald (Humans), the only use of Destruction for the Dwarves is to deal 14 damage to an Angel with a spell, while Ice deals 30 damage to the remaining troops from hand, and the damage is greater than with the Destruction spell. If the Dwarves had a Summoning school, the impact would be much more noticeable.
Perhaps it could be given a Lightning spell. Dugald, on the other hand, has 2 useful schools of magic.
The situation is even worse for Hafiz; he also has 3 spells like Ibba, but doesn't even have a single Ice spell.
If we judge on a scale of 3 or more skill increases, Destruction magic is purely a support magic for a hero focused on physical attacks. You take Destruction and its perks at the last levels, and cast debuffs. By level 15-20, any hero will have 4+ skills, and magic doesn't play a significant role in that case.
In cases where you have a high magic skill (15+), Light and Darkness simply become less effective, and that's when inexpensive spells come to the forefront.
Such as mass Haste at 150% or Attack Boost at 22.
Of the expensive spells (15 mana = 3 skills), Resurrection and Restoration justify their cost, and the further you get into the late game, the more control spells become effective.
Spells like Holy Word are generally not worth their cost, unless you manage to repeat the situation from the duels, where you encounter a single stack with an Expert school.
At the same time, there are spells like Teleport and Vampirism that are very strong and worth their cost