If you only look at the heroic lineup, the Alliance undoubtedly has the advantage.
The key is that there are many top-tier heroes, including Gedwyn among the six Silver Saints, as well as several Gold Epic heroes participating in the battle.
On the other hand, aside from Orgrim and Ner'zhul, the rest from the Horde side were mostly insignificant.
However, what they lacked in numbers, they made up for in strength.
Ner'zhul had also felt that the enemy's lineup was formidable, and he initiated his Hero Skill right from the start.
Ner'zhul (Shadowmoon Chieftain): "Storm, earth, frost, and flame, spirits of the elements heed my command!"
Hero Skill—Council of Draenor Elementals!
Spirit of the Storm, Feltrom.
Earth Fury, Polrut.
Frost Walker, Esgost.
Flame Giant, Surutael.