If this "average joe" doesn't have enough time or inclination to make a tanky build to solo and harass players and keep them from scoring points, he probably doesn't have the time or inclination to make a viable dungeon build either.
If this "average joe" doesn't have enough time or inclination to group up with a small team he probably doesn't have time to make an arena team on WoW, is probably not interested in pvp anyway.
But think about what you're saying about this zerg for a minute. Ok, we have a zerg, this big massive rolling ball of death - but WAIT! It can only be on one place on the map at a time. The map is HUGE, it's GINORMOUS, it's a BEAST of a map. The matches last for a full week, people are zoning in and out of WvW all the time. They do not zone in directly to the zerg's location, they have to find them first.
All these players, looking for this zerg. All these opportunities for small pvp play.