PvP requires team based play. Most people seem to treat it as one on one... and it doesn't work that way since the player position is determined client side.
It's more about how classes in FFXI have some amount of synergy with eachother. It's not like WoW where every class has all the basic tools they need to survive without any support. Preists may be top of the line healers for instance, but they also have many effective damage and support abilities. Every class in WoW stands on its own, whereas some FFXI jobs only really show their stuff when there are other people around. A good team fight in Ballista is way more exciting than in WoW, where team fights usually become extremely spammy where basically the two groups are standing outside of a circle I refer to as the "death zone" where everyone is spamming their spells and attacks. WoW has much more emphasis on the individual where FFXI is centered around groups.

One isn't inherently better than the other and I'm not bashing WoW here. FFXI and WoW can both have enjoyable PvP, but the style of each is very, very different from each other. 1v1 just isn't very interesting in FFXI, but a 6v6 team fight is very exciting.