Am I surprised by this? No, not really. I definitely give these two huge props because fighting one boss for 3 hours would drive me insane, but Loatheb is not exactly challenging. In fact, I think bringing fewer people to the encounter would make it dramatically easier for a Healer. This isn't the first time Loatheb has been knocked down a peg by a hilariously small group, either. Back at level 60 when Naxxramas was a 40-man dungeon, Loatheb had been 5-manned by a Warrior, a Warlock, and 3 Shadow Priests.
Currently, Loatheb hits like a wuss. The tank hardly takes any physical damage at all. Almost all of the damage in the encounter comes from an AOE called Inevitable Doom. Shortly after combat starts, the boss starts casting it, and as time goes on he starts casting it in shorter intervals. Every 15 seconds is as fast as it can get, and it does about 4,000 damage. This becomes scary because of his Necrotic Aura. It makes all healing spells do 0 healing for 17 seconds, and then there is a 3 second opening where you can spam your heals before the aura returns.
When you have a full raid, the damage starts to build up. You get to a point where you can't heal everybody, and then the Healers start to worry. Panic sets in, everyone starts mashing their cooldowns and freaking out because the raid is about to die a very slow death. Except... not. Even when you have a bunch of deaths, it's pretty hard to wipe on this fight unless your mana disappears. Mostly, when you lose all of your DPS, you decide to just let yourselves die so you can start over and try again, so the tank doesn't take an hour to finish the boss off.
A tank and a Holy Paladin is a great pair to duo this fight, because of Bacon of Light and the Paladin's strong single target heals, and when the Necrotic Aura is up you have Sacred Shield to lend a hand. What's going to kill the two? Certainly not the physical damage, and definitely not the Inevitable Dooms every 15 seconds. Even if you took two of the dooms while under the effect of the Necrotic Aura, that's only 8,000 damage. What is that to someone in a raid at level 80? Not a lot. The tank will be taking physical damage as well, but not much, and raid tanks on the low end have 30,000 HP. The only way you could die here is from boredom.
Again, don't get me wrong. These guys doing this is awesome and not everyone would have the patience to do it, or the concentration to do that for three hours. I'm just saying it's not surprising that Loatheb was the one to get punked.
PS: Don't blame me for their music choices, kay? Thanks.