Theramore isn't about horde advantage.
The whole existence of theramore from begining was advantage for alliance, the destroying of Theramore was only making equal for both factions, this wasn't destruction of any capital city, but Theramore hadn't any counterpart for horde....
Wow, people still crying about Theramore? It's destruction was the sanest thing the Horde has done since letting the Tauren join them. Is there factional favoritism? Fuck yes. But it was given to the Horde first and now, in response to that, they have to match the odds with the Alliance. Still I think the Siege of Orgrimmar was taking it too far. Way too far. But in the end, it's not gonna matter cause when they pissed the Horde enough they'll go back to the Alliance.
Most of that lore isn't directly relevant to the playable Horde. As for the Alliance? It suffers a number of issues but they're directly linked to the disproportionate amount of focus that the human race receives at the cost of pretty much all of the non-human races within the faction. That's the real reason as to why the faction is stagnating, not that the Horde is somehow getting more stuff - because it really isn't.