In my experience the horde “bias” comes mostly from most alliance being too stubborn and too set in their routines.
Horde is as crap as alliance in pvp if people would actually play the game and not start moaning about everything from climate change to bad knees before match even starts.
And whats with the people on alliance joining to bg’s at 120 wearing legion quest rewards is that horde bias too?
Most bg’s where alliance loses has nothing to do with horde “bias” its almost always caused by stupidity and getting too comfortable to idea of winning when things go too good in a bg.