So we know that the Elemental Dissonance of Book 2 was caused partially by Fire and Darkness— these were the two elements specified— being weakened by the deaths of Akriloth, the Great Fire Dragon, and the Darkness Dracolich; but what about Ice? Cryozen died during Book 1, too, and he was the Great Frost Dragon. Shouldn’t that have made Ice weak, too? It’s possible that it did and they just didn’t mention it, but then I don’t think they would have mentioned that Darkness was weak, either, because the problem with Wargoth started with Fire.
So, thoughts:
1) Writers just forgot to mention it (possible, but no fun and, even if true, doesn’t give an in-story explanation)
2) Xan just didn’t mention it. Possible, even likely, considering Xan was aware of Akriloth and the Darkness Dracolich, but not Cryozen. In this scenario, the Realm of Ice is as weak and vulnerable as Fire and Darkness.
3) The Realm of Ice avoided vulnerability due to Cryozen’s heir hatching. Now, Akriloth’s heir hatched as well, but clearly wasn’t enough to make up for the imbalance caused by their father’s death since the Dissonance happened anyway. The difference for Cryozen? Vilmor. We know that baby dragons with DragonLords can assume their adult forms and access adult power, so it makes sense that Ice is at least somewhat more well-protected than Fire.
Additionally, on related train of thought, baby dragons take centuries to grow to their adult forms naturally. Two hundred years is still adolescent, if we use Nythera as a guideline, and she’s half-dragon so that might impact how she grows (though she implies she ages in dragon years). Meaning, the Realm of Fire still should be weak, right? Because baby Akriloth is still... baby Akriloth.
(The Realm of Darkness may have recovered because it wasn’t the death of a Great Dragon but the death of a lot of Darkness elementals, including the Mysterious Stranger, attached to Fluffy that caused the imbalance. That may have already been compensated for, who knows. We don’t have a way to estimate one way or the other.)
Anyway, just some thoughts I was having.