DRG quests 30-50 reveal that Azure Dragoons are a cut above regular Dragoons and can perform more powerful feats that require channeling of Aether via Nidhogg's Eye (e.g. Dragonfire Dive). After the events of defeating Shinryu in Stormblood, both of Nidhogg's eyes are annihilated by Estinian, yet he and we presumably maintain our Azure Dragoon powers. How? Moreover, Life of the Dragoon seems to be a channeling of specifically Nidhogg's Aether, as Nastrond seems to be a Geirskogul that's steeped in his crimson Aether.