Heroes 5.5 WarGame Edition - Tactical Edition.

Isn't this the reason why the game developers gave different bonuses to the "attack" (5%, 10%, 15%) and "defense" (10%, 20%, 30%) skills, and perhaps it wouldn't be worth making them the same (in both cases 10%, 20%, 30%)?

No, not because of that: that's why I wrote about "large numbers." While 10-30% are small numbers. Besides, defense is even more powerful than attack, even with equal numbers (countering attack and defense is not the same as power versus weakness in classes).