The Horde possess some of the great Shamans on it’s ranks, hence their Elemental culture is strong and well tied within some races like the Orcs, Mag’har Orcs from the Blackrock, Warsong, Frostwolf and Shadowmoon clans. Likely we do have the Taurens and the Darkspear and Zandalari Trolls.
Despite it, the Alliance is seem to be fiercely righteous and punishing towards the Fel and Dark Powers.
Not all the races and not everyone from the Stormwind society. Varian himself fought side by side with warlocks and didn’t show any kind of prejudice.
Likely, on the Alliance side we possess a strong connection to the Light. We are emboldoned by the Church of Light presence at the very center of Stormwind. Lorewisely, the Stormwind society possess many Clerics or Priests within their ranks. And for sure we are some of the most powerful Orders nowadays, as our High King, Anduin Lane Wrynn is one capable of doing even powerful that most of the other Priests don’t.
Also we do have an powerful legion of Paladins at our disposal that the Blood Knights of the Blood Elves surely wouldn’t wish to met on a battlefield.
Some of the most powerful mages who live today are also humans, like Jaina Proudmore, Archmage Modera and the Archmage Khadgar.
So our acknowledge of the Arcane powers could beat even the Sin’dorei.
To end this conversation we have the most powerful Druid at our side, and the connection of the Night Elves to the Nature is unbeatable. The Taurens are also a great ally, but Darnassus were someday setted on a tree, and it’s whole civilization like to live near at some kind of green and animal beings.
Actually, the Dwarven and Night Elven races produces a lethal contigent of Hunters and Shamans and Sentinels and Priests, respectively.
The Dwarvens have the Dark Iron, Wildhammer (by far my favorite clan) and Bronzebeard clans, which one producing powerful Priests or Hunters, or Shamans or Warriors that the Alliance could count on.
The Alliance is supreme.