Jason

Again, TheBestWarGames's assigned writer for this anime hasn't read the light novels/ translated web novel.

The manhwa adopted the webnovel. The Anime is adapting the webnovels. How the anime adopt the webnovels is frankly more true to the webnovels than the manhwa was. But this narrative that the anime is 'changing' things is not accurate, it's adopting the webnovels differently than the manhwa. It hasn't introduced material that wasn't in the webnovels. It has rearranged some things to be introduced to the audience in a sequence that introduces the audience to characters other than Jinwoo earlier; basically it is sprinkling side scenes that lead up to the jeju island arc earlier than the webnovels, which kind of just dump all of the jeju island leadup in one big lump, rather than spread out in earlier material.

More, earlier intro of that lead up makes sense, because the author would have gone back and added those scenes as foreshadowing if they had the chance-- except they wrote the original material as a webnovels. So it wasn't until they had figured out what they were gonna do with Jeju island that they could insert other characters.

This is kind of skipped over in all the lore dumping, and is not obvious to the characters themselves, but if you played DA1 and Inquisition, the reason Davrin survives the first Archdemon is straightforward.

Which is that the reason a Warden had to die in previous Blights is that they become the temporary vessel of the soul of the Elven God they are bound to-- or did, when the Evanuris were trapped in the Fade. It's the same trick Corypheus uses in DA Inquisition to hop around bodies between blighted and red lyrium infected individuals-- and each previous Blight the ArchDemon has been possessed by the soul of the Evanuris it was tied to.

This is how in DA origins Morrigan and the main character are able to kill the ArchDemon without a warden dying; they capture the soul of the Evanuris in question in the unborn child Morrigan conceives prior to the battle, a process that seemingly (if you choose this option and meet the kid in DA Inquisition) cleanses the soul of the Evenuris in question of the Blight. So now that we also know Flemeth was also Mythal, mother of most of the Evanuris, we know why she was so invested in claiming the soul the possessed the ArchDemon in Dragon Age Origins, to the extent she set Morrigan up to be in place and make the offer to the Warden.

So with that explanation-- Davrin didn't die to the ArchDemon because Ghillin'nain's soul was not possessing the ArchDemon, it was inhabiting her true body. Each Blight was effectively a jailbreak by one of the Evanuris by the method of blighting their soul-bound dragon until they could soul jump into the dragon's body, becoming an ArchDemon. ArchDemons could not be killed without Wardens, as prior to the advent of Wardens the Evanuris in question could just hop to the nearest Blighted vessel, restore the ArchDemon's body, and hop back into that body. But a Warden fighting the ArchDemon would be the nearest Blighted vessel, and if the warden died while possessed, the Evanuris dies too.