Great posts, especially the link to the EQ2 forum thread. I would like to make some minor observations, however. Green ^^^ Heroic mobs are soloable. As a level 33 Paladin, I regularly seek those mobs out over any others, as they offer better XP and Loot.
I've managed to solo a Blue ^^^ Heroic after LU13, but it was very hard. It seems there is more to take into consideration than just color con and arrows of the monster, but also the "class" as well. Mage type monsters seem to be the easiest, as I can interrupt their spells and resist the ones that are actually cast, plus their defense is the lowest. Fighter monsters are the hardest with the large defense and hitpoints. I usually run out of power against Green ^^^ Heroic Fighter mobs and it becomes a slugfest at the end.
A guildmate (level 28 Paladin) and I (level 33 Paladin) were down in the lower parts of Stormhold yesterday, duoing and working on his AQ3 when we discovered the Maelstrom Vault. I've been in that area many times before to help others with their Relics for Aluard quest, but I don't recall seeing it before. We went down there, spoke to the sword, and went through a series of elemental battles. We did fine until we got to the Ice Storm elemental, a Blue ^^^ Heroic and then we died. This would again support my observation that not all Blue ^^^ Heroics are the same or for that matter, any mob of the same con color and arrows. We came back with a level 27 Guardian and a 21 Shaman who happened to be in Stormhold at the time and decimated the Ice Storm and the 8 Blue ^^ mobs that popped up next.
In addition to the "class" of mobs adding variations in difficulty, I would also agree that "named" mobs seem to be much more difficult as well.