The survivability so far. They are all tanks so even if you loose agro on the main, you have a lot of time to do something about it. They are not going to die in one hit or five, or ten. They are all healers, so I don't have to worry if my healer goes down if I am going to survive the encounter. They can all rez, so even if half my group dies, I don't have to make a corpse run with half a team. Everyone being the same race/class makes quests a bit easier, I don't have to browse six different quest reward options or come up with six rotations to optimize dps. Heroic opportunities seem to be a bigger distraction than they are worth, but with six fighters they get chain cast pretty easy.

I can see how having a Guardian and Templar to the party would help with some extra utility and buffs and I may power level one or two up if I find I need to.

As far as min/maxing goes, I feel that is uncommon when it comes to boxing. Paladin and 4x Shaman is the staple group in WoW next to 5x(same class, druids, warlocks, hunter) groups. Few boxers play an optimized group because it overrides the ease of use of a matched team. In the end, one or two extra buffs just are not worth the hassle.