Maintenance for the week of December 16:
• PC/Mac: No maintenance – December 16
• NA megaservers for patch maintenance – December 17, 4:00AM EST (9:00 UTC) - 12:00PM EST (17:00 UTC)
• EU megaservers for patch maintenance – December 17, 9:00 UTC (4:00AM EST) - 17:00 UTC (12:00PM EST)
Close to 6 million health points crammed into that little red bar do that if you hit them with the proverbial cotton ball (as which every player damage skill except radiant destruction could be considered, if you believe forum dogma).
They may have 6,000,000 HP but they are still immortal. Even when down to zero health they will just keep on fighting. They have to as 6,000,000 HP really isn't that much, Vet Pledge bosses at VR12 have 2-3,000,000+ health are require tactics so DPS is lower.
If you got a group of DPS each doing 10k on average it would take minutes to down a guard, which is totally doable, hence why they are immortal and can do absolutely crazy damage.