Reiterating on what I said in Leave "Loot Piñata" events out of Capital Cities, and as Phenomenon stated, this sort of events has no business in capital cities. Stormwind in large realms was very literally inaccessible for a while when the portals were up there. I would really welcome an explanation as to why the Horde (rightfully) got Durotar, but the Alliance has to deal with the event in Stormwind when several great alternatives were right there.
Moreover, this sort of event just seems nonsensical. Nothing much seems to have been learned from the Diablo promotional event. It’s obvious that there will be massive crowd surrounding the one spawn location for these event mobs, but the design philosophy remained unchanged, so all it really is is a race against the server to get a tag in, for a very random drop.