Firstly, magic, and especially mass spells (in Darkness and Light), are very helpful in this case. I always use them.
Secondly, a 20th-level Necromancer with expert education and in a real game with artifacts will rarely have an attack of less than 20.
Thirdly, if a 15-20th level Mage starts making mini-artifacts, they will be left without upgrades and the Mage Guild, because at this stage of development, there are still few resources.
Of course, mini-artifacts and the partial ability to block enemy magic are a strong blow to any opponent, but in principle, it is not fatal for a Necromancer. Also, don't forget about the chain of elements.

Dear Sir, it seems we have a slight misunderstanding.

I am not claiming that the Dark faction has nothing to counter the Mage or the Dwarf. I was simply opposing the opinion of Nightly Edelweiss, expressed in message #501 in this thread, in which she claimed that the Dark faction's army is just an addition to the hero, and developing the hero as a pure Chaos mage + a corresponding set of artifacts that enhance elemental damage guarantees the opponent will be facing a formidable foe:smile51:

I simply clarified the hero's development, parameters, and level to show that this is not the case.

Regarding developing a hero against the Mage and the Dwarf, I will write about it later.