I can also see the IE being divided between supporting Thera and fighting Dragons and supporting Dragons against Thera. That will enlight why there is a dragon in the council of one Tir (pro Elf/Dragon alliance) and none in the council of the other (pro Elf/Theran alliance).
I thought Tir nA nOg was the legacy of the Blood Wood, not anything to do with the Therans???
The high number of elven birth in Ireland suggests there was an Elven nation there during the Fourth Age. So we can imagine it was among the realms ruled by the Blood Wood before the Scourge (one argument against this is that, if Serethea, modern-day Latvia, was in the
Western Kingdoms, it somehow suggests the elves weren't aware or didn't care about places west of them).
However, Tir na nOg Seelie Court is different from the Blood Wood Elven Court, since it includes not only elves, but also spirits, pixies, leshies and the likes, who gather on some sort of metaplane. Maybe the island wasn't an elven nation, but the realm of "fairies". Elves and the Elven Court would have moved over there late in the Fourth Age and the fairies offered them those refugees a shelter. That could explain there seems to be far more fairies than elves at the Seelie Court.
Though Tir na nOg council of stewart, the gathering of the Danaan families, could be compared to both the Blood Wood Consorts and the Theran Empire Conclave, so can most oligarchies in history. On the other hand, there are eight major clans, the Danaan mór, just as Queen Alachia had eight Consorts in the Blood Wood (however, it's Alachia who set that number, there used to have more or less before).
But it also worth noting that while the major clans are known to have ruled Ireland since prehistoric times or so, clans of Norman ascent established in Ireland since the Middle ages (Fitzgerald, Burke and Butler) also belong to the Council of Stewarts. So the historical connection with the Fourth Age may prove thin. They nonetheless had a number of elven birth just as high as the other clan (save the big eight). There may be an explanation, like some Norman family line going back to Shosara, or some wandering Immortal Elves fathering one of their ancestor.
Tir Tairngire Council of Princes may also be compared to the Blood Wood Consorts. The number of elven Princes also was eight: Aithne Oakforest, Sean Laverty, Jenna ni'Fairra, Ehran, Jonathon Reed, Maria Cinebal and Dar Varien, plus Sosan Naerain (strongly hinted at being the former Queen of the Blood Wood, Alachia) or Lugh Surehand (depending which of those two you want to piss off by insinuating he/she is a consort).
There was no dragon on the council at the founding of Tir Tairngire. As far as the telling goes, it was Surehand own decision, strongly resisted by all the other immortals, except Sean Laverty. So maybe immortal elves and great dragons hadn't discussed the foundation of Tir Tairngire beforehand. But there might have been some sort of agreement to have a dragon overseer on the council, and the princes were simply opposed at the seat going to Alamais' brother. It seems also Lofwyr got to choose who would replace him when in left.
It's difficult to assess Hestaby position, since she first appeared to block Tir Tairngire military forces moving in Mount Shasta area. If the IE knew there was a great dragon lair in the area, they would have knew the invasion was meant to fail. Had they discussed the importance of Crater Lake with dragons during the Fourth Age and the need to watch over it, they could have know one of the dragon was to set a lair near (there's less than 200 kilometers between Crater Lake and Mount Shasta ; it's next door to a magical flying lizard). Maybe they weren't sure Hestaby was awake or survived the "downhunt" and sent military troops to see if something happens.
What I found to be the most telling point is the fact Tir Tairngire head of state is no king, only a
high prince. Would have Alachia be Queen of Tir Tairngire if the other IE hadn't barred her from it? Or does the crown officially remains in Tir na nOg, as an "host" of the local fairy court?
Alachia obviously has the pivotal role. She was the Queen of the Blood Wood during the Fourth Age. In the Sixth, she is (or so it seems) only one of the Prince of Tir Tairngire, and an advisor to the Queen of the Seelie Court. She is also at the head of the Atlantean Foundation, but
Dawn of the Artifacts revealed she forged the Atlantean/Theran codex she showed to the Mystic Crusaders. So Alachia is actually pillaging the Theran legacy. Call that an ally.
The true heir of the Theran Empire seems to be the Heavenherds tribe in the Zulu Nation, where Thera established their colony of Aznan. "Heavenherd" was the title of Thera most powerful mage, who were all humans or elves. The Zulu Nation, on the other hand, is an Elven nation, and the Heavenherds tribe is known for including really only elves. According to
Augmentation, the Heavenherds tribe knew magical rituals designed to lengthen the lives of the most worthy members of the tribe, by binding them to something called "passions" (sounds familiar ?). Frosty comments both Tir na nOg and Tir Tairngire "wooed" the tribe.
I think at some point the Therans formed one group of Heavenherds, sent to Aznan and tasked with preserving Theran lore and knowledge during the Fifth Age. All of them were elves because they had a longer lifespan to start with, with rituals on top of that. But it may not have been enough for any of them to survive until the return of magic.