Whoever says Legion was an Alliance expansion would have to recognize that CATA, MOP, WOD and BFA were horde expansions.
If these are protagonists belonging to the faction, it would be so.
But I don’t think so, when the main plot is about a faction in itself it can only be said that it is an expansion of a faction.
Thrall in CATA represented Azeroth, you were his plot as a character,The same goes for Velen in Legion more than anything else in Argus, it was his story.
The plot in an expansion deals with the conflict and it has already happened twice that the conflict has been within the Horde.
We have already had two expansions that smell like red, blood and thunder.
For some reason none have smelled blue and gold.
None of the Alliance has tried to find itself, what it means to belong to the Alliance
We have always been clear, maybe too much.
Another issue with the Alliance Characters is that they are neutral by nature or rather the plot has accommodated them in that default position.
The only character clearly Alliance is Genn.
I am sure that you as a member of the horde do not feel uncomfortable having with you the great majority of leaders and characters of the alliance.
You know he was not killed or abandoned halfway.
The Alliance on the other hand can never Lower the Guard and really trust except with Thrall or Baine.
and not because they don’t smell like the horde but because you know they are good people.