Flying mounts didn't kill world pvp in WoW, people not wanting to do world PvP in WoW killed it. All the proof you need is when the sunwell patch went live and every high level player on both factions were forced into a tiny island, all that happened on my pvp server were a handful of gank squads killing people trying to do dailys and running away from anyone actually wanting to pvp, everyone else just ignored each other. or you could look at any summoning stone location for raids, the only pvp that happened was when a full raid or more was present against 2-3 others, anything close to equal numbers just meant everyone ignored each other.