A (Highly Theoretical) Look at the Cycle of the Eras

[Teiren]

Well, be careful about analyzing fights about difficulty based too much on gameplay. The fights are only there to tell a story. That is, they have to make stuff like the Nidhogg fight in The Aery a braindead joke so even the most incompetent players can get through it.

You don't seem to be doing that, but I'm just giving a reminder. Thinking about it from a story perspective, just like you are:
At the Aery, while he is crippled compared to what he could really do in the past or at full power, remember that he's still quite strong. Not only does he have a powerful flame breath but he also has considerable powers of telekinesis (moving the fire orbs and lifting people), which seems amazing to me for a dragon or really any creature. Maybe it's not telekinesis but something else that I don't understand? It looks like some kind of shadowy energy when he lifts people to try to crush them. Anyway, not only that, but we were only barely able to survive his Massacre attack thanks to Estinien's manipulation of the Eye. Though what do you mean by, "not even using his own power?"

I don't think the final fight against Nidhogg will be with him at full power. Based off the lore that I understand, it just doesn't make sense that we could stand up to him or do anything at all to him if he's at literally 100% power. I never did the Final Coil of Bahamut in ARR, though I did complete Second Coil recently, but wasn't the final encounter there against an alpha version of a rebuilt Bahamut? And that's the only reason we were able to stand up to him? Please correct me if I'm wrong as I've shied away from that story.

Anyway, I think there'll be some shred of Estinien left inside that'll hold Nidhogg back. We don't know the story yet. For anyone that knows Warcraft lore, it may bear many similarities to the relationship between Arthas and The Lich King.