The Horde has never actually been the underdog. In Warcraft 1, a single part of the Horde destroys Azeroth and razes Stonewind Keep. In Warcraft 2, the only reason the Alliance don't lose outright is because Gul'dan split the Horde's forces at a critical moment. In Warcraft 3, you never actually get the feeling that the Horde was struggling--it only ever seemed that you were being *told* they were, and that the humans were being mean to them for the whole genocide thing.

Then in World of Warcraft the Horde becomes a monolithic international organisation, essentially Hordecorp, and they go from strength to strength. TBC arrives and is almost all about the Blood Elves, then Wrath hits and we're told--instead of shown--that Garrosh "never actually won a fight in his life" Hellscream is apparently a war hero and tactical genius.

Then we get to Cataclysm, and in the name of gameplay balance the Horde rides roughshod over the Alliance everywhere you turn. Then we get to Mists of Pandaria--and apparently the same gameplay equality that saw the Alliance lose quest hub after zone in a series of ridiculous defeats (Andorhal lol) is no longer a concern and we lose Theramore as well.

It seems like the gameplay is more important than the story when it benefits the Horde, but the story is also more important than the gameplay when it, too, benefits the Horde.

As long as they've ever been playable, the Horde has never been the underdog. There was only Lord of the Clans, the novel rushed out to explain just why Thrall was the new Warchief and why he wasn't anything like the old Horde leaders.