Heroes 5.5 WarGame Edition - Tactical Edition.

And the shamans actually have it! The Daughters of the Sky can quite easily cast a chain of lightning, which cannot be explained by pharmacology.
Orcish warlords don't cast magic (within the five factions), but it seems it's not due to an inherent inability. Perhaps their leaders are simply not smart enough (unlike the shamans, who dedicate their entire lives to connecting with the father-sky and mother-earth, rather than fighting for power and engaging in skirmishes with the prospect of becoming the clan leader).

They don't have full-fledged magic. In WGE, they don't have chain lightning, speed, or slow. In fact, only one of the three types casts spells, with primitive spells like evasion and general exorcism. After a mana boost, teleport and berserk become available. Any of these spells can be reduced to tricks and tactical maneuvers (like goblin traps and magic disruption). None of them depend on witchcraft, and this is very important. And these "tricks" are usually "cast" by a group of shamans, i.e., these are social "spells," and a lone hero naturally cannot do anything like that.

Perhaps their leaders are simply not smart enough.

Among their leaders, there are also shamans who also "for some reason" don't cast spells.

In general, from the point of view of an orc, humans are cowards, weaklings, and fools. They look like freaks, in a word, they are "small-toothed." They are useless without armor, not adapted to survival in the natural environment, they worship some made-up god, a dragon of light, which no one has ever seen in nature (well, elves and dwarves at least worship real dragons), and most importantly, they don't understand pharmacology, some even deny its very existence. Therefore, the assumption that shamans are humans was very surprising