Heroes 5.5 WarGame Edition - Tactical Edition.

Demons, on the other hand, are good at defense. Mages study martial arts. What's with all these possible and impossible skills!?

Mages have 2 problems with attack. The first is conceptual. In attack, there is a branch dedicated to direct hero attacks (heroic attack with increased damage, stunning, weakening); this is not really suitable for a mage. A mage will never engage in melee combat because he has magic (and mana).
The second is a balance issue. In attack, there are the perks "shooting" and "battle frenzy." Both work great for gremlins (low-level archers). In addition, there is a specialist for gremlins - Hafiz. What do you think is Hafiz's strongest base? Naturally, attack. Therefore, if possible, the hero should have this base from the start. Otherwise, he will strive to get it throughout the game, without any alternative gameplay. But if attack is prohibited, Hafiz has no other choice but to be content with machines, which are actually better suited for him in terms of non-gameplay meaning.

Added 2 minutes later

"leader's order" is almost a duplicate of "inspiration."

The "order" skill is very important for orcs because it removes blindness and grants "bloodlust," just like other warcries. "Inspiration" does not grant "bloodlust." And "prayer" is not needed in leadership because one of the types of orcish shamans casts it in the Warlord's Guild.