This argument seems to be based on the assumption that it is not just being active in and of itself that makes a story valuable, but that getting to be more active than somebody else inherently makes it more valuable. I disagree with that premise.
Both faction stories should be active and coherent. Making the Alliance’s story more active and coherent is something that Blizzard should do. Making the Horde’s story less active and coherent at the same time, however, does not make the situation better for anyone.
If Blizzard is not capable of making two faction stories active and coherent at the same time, then they should not be writing a two faction game.