They're definitely writing it assuming the player shares their sympathies, rather than writing the characters in a compelling way to make the player gain the sympathies.
The Thorignir are a subset of stormdragons who were loyal to Odyn and helped protect the Aegis of Aggramar. When the Legion invaded, some defected to the Legion and joined Skovald, but some stayed loyal to Odyn and fought against the Legion.
In the scenario, Vyranoth literally does nothing but yell that the Thorignir don't have to obey Odyn, (image here if wanted
https://i.imgur.com/emPV7nU.jpg) and this apparently is enough to get them to fly away to abandon the Halls of Valor and fly to the Dragon Isles. This only makes sense if the Thorignir really wanted to leave but were somehow too stupid to realize they could, and could have for millennia.