Ganking is used in pvp to refer to any unfair fight. People of equal level and gear and skill often gank each other and corpse camp each other. Many people have no problem with that. That is the sort of ganking that blizz set up pvp servers for and defends. What people here are addressing, and what blizzard hasn't addressed, and what you are pointedly ignoring to just point at something vague as gospel on the subject, is the specific type of ganking where there is no chance whatsoever for one of the players involved, because the game engine doesn't allow them a chance. There is no scenario where a level 90 in reasonably appropriate gear will be bested by a level 58 at the dark portal. 30 levels of disparity is something that the games mechanics just don't allow you to make up for.
Well if you wanted you could engage in pvp with someone, or even attack the level 90 who would then handily be able to one shot you as before, or just permaflag yourself like some people do on non pvp servers. The idea of a pvp server is that pvp should be something you engage in, a player getting repeatedly oneshotted by someone who they have no means of interacting with at all is not engaging in pvp.