I am Brash AKA Bagar AKA Bladget from Red Death, Horde.
I had a gnome warlock but chose not to get it all the way to twinking levels. The reasons are as following:
1. As soon as Alliance has a chance, they will camp as at graveyard. Not as a tactical maneuver, as to capture flag easily, but purely for fun. Ignore the objective and kill us. These occurrences are rare, thankfully. We only did the same thing in a response, never first. When someone of us does suggest we do it, I am the first to stop fighting or quit the battleground.
2. We don't complain on the forums when people switch to Alliance from Horde.
3. The free action potions and "flag carrier" builds were introduced in the bracket first by the Alliance. I didn't even know those are a thing before Fc AKA Obi AKA Mockingjay. Even now I only use my FC build on death knight when outnumbered, or need to make a point, as with camping, mentioned above.
4. Alliance will stop queueing as soon as they start losing, even when they have numbers. Don't believe me, ask Smuch, leader of the Alliance twink guild, or Hyper AKA Premonition. This wasn't the case before. Once, I myself was queueing about 5 games in a row as a single twink with levelers agaisnt an Allinace twink team.
5. Alliance have a 32 level Horde character. With it, they whisper low-level Horde players to queue battlegrounds, as to provide an advantage to the Alliance.
It is true that Alliance side is in a decline currently. However, I am completely positive that this is their own fault.