One of the subjects that pops up regularly in the MMORPG blogosphere is that of the holy trinity, the combat system based on tanks, healers, and damage dealers. Many people have grown dissatisfied with that system, so frequently there are blog posts with various ideas of improvement, or ideas how MMORPGs could abandon that system. I was playing a turn-based fantasy strategy game this weekend (Fantasy Wars), and that made me think how "tanking" worked in strategy games, in reality, and in MMORPGs. And I think that tells us a lot about the holy trinity.
In Fantasy Wars you have some units you don't want to get hit, like archers, or a healing priest, or a mage. So what you do is to build a wall of heavy infantry units (tanks) in front, and because these units have a zone of control, and enemies can't simply pass through, the enemy is forced to attack the tanks and not the squishy units behind. Your wall needs to be wide enough so that the enemy doesn't have enough movement points to simply run around it. While still a game, and thus not totally realistic, this is a lot more similar to a real battle with infantry in the front and archers in the back than the MMORPG system.
In MMORPGs with the holy trinity system, a tank fulfils the same basic function: Standing in between the enemy and the squishier group members. But he doesn't do that by (virtually-)physically standing between the two. In fact in many MMORPGs characters and monsters can run through each other, there is no collision control, and there is certainly no zone of control hindering enemies movements. Furthermore movement in MMORPGs tends to be unrealistically fast and agile: It is pretty certain that a knight in shining armor would have considerable difficulties to "circle strafe" in real life at the same speed that characters do that in video games. Thus with movement being too fast and unhindered, the tank cannot stop the enemy by positioning himself in front of the healer or mage.
What a MMORPG tank does instead is "taunting". Apparently nearly every enemy in a MMORPG, from a mindless slime to the Lich King himself, will always attack the guy telling the "yo mamma" jokes. Even if he is currently right next to a squishy, high-danger target, while the tank is deals less damage and is harder to hit.
Even if we explain away the "taunting" as some sort of magical mind control, there remains a major difference between tanking in a strategy game or real life and tanking in a MMORPG: The ratio of tanks to squishies. In a MMORPG you can have one tank protecting 3 mages and a priest, even against multiple enemies. That obviously wouldn't work if he had to stand between the enemy and the other group members. For a more realistic tanking situation your group would more likely have 3 tanks, 1 mage, and 1 priest. Or in a larger group 5 tanks, and 2-3 mages and priests each. Unless all your dungeons are narrow corridors, where one or two tanks can completely block the way, you'd need about half of your group as tanks if tanks would work by standing between monsters and the rest of the group.
While this sounds very much like a completely hypothetical and theoretical exercise, there is nevertheless one lesson to be learned here. By having gone from a war or war game situation with multiple tanks to a MMORPG situation with only a single tank, the responsability for tanking has become extremely concentrated onto a single person in groups and even raids (the "main tank"). The tank is held responsible for aggro control, up to the point where in a pickup group some dps unable to reliably target the mob with the skull floating over his head or to use /assist will *still* blame the tank if a mob attacks him. Or blame the healer of course, another case of all the responsability for one function concentrated onto one character in a not very realistic way.
Thus while I am not offering a different system than the holy trinity here, I can very much offer a basic condition for a different system to work better than the current one: Responsability has to be better and clearer shared between the group members. Maybe some multi-tank system with slower movement, collision control, and zones of control would work, but we appear not to be quite there yet from a technical point of view.