The problem with Horde-bias is that we have several videos with jabs towards the Alliance (from the developers at different BlizzCons), actual belittling on a Q&A, several questionable inGame decisions (like hiding the Horde emblem under Varian’s grave) and the infamous Horde concert where people harassed Alliance-players and the former president had to post an open apology.
Horde-bias is a very rabbit-hole’ish discussion but in the end they are somewhat favored to a degree. It doesn’t help that the majority of the player base is Horde by now, at least the competent ones.