In Heroes of Might and Magic V, the danger level is not displayed for the Hammers of Fate! What should I do?

Winner, do you advise focusing on developing Dark Magic first?

Not always. It's practically useless against the undead. I would rank the three magic schools in terms of usefulness as follows:
1. Dark
2. Summoning
3. Chaos
Light Magic is separate here: it is universally applicable.
So, Chaos Magic allows you to defeat enemy troops if the danger is Very Low to Medium. If there is a hero, they may have such an unpleasant thing as "Magic Resistance".

Summoning is more relevant with large armies. In addition, a summoned creature that can attack while it is being killed is more useful than a single spell or even an area-of-effect spell.

Dark Magic, thanks to "Berserk" and "Enslave," allows you to destroy practically an unlimited number of neutral creatures. It's more complicated with a hero; in addition to "Resistance," "Dispel" is also dangerous here. But it is quite possible to defeat a hero with High danger.

Light Magic will provide victory with equal armies. If you have lost many troops, "Divine Retribution" will be useful. In general, the danger that can be "neutralized" with Light Magic is Medium and sometimes High.

This is what the danger system doesn't take into account. But combat machines, Readiness, and Devil's Strike also reduce the enemy's danger. On the other hand, if the enemy has "Counterspell," you will have to skip turns until an entire unit-caster absorbs the impact of this unpleasant ability. If there are none, then you can forget about magic :(

By the way, it would also be a good idea to rename the topic to "Danger System" and move it to another section ;).