Major plot hole with Heavensward ending (Spoilers, duh)

[Allyrion]

No matter how insain he is atleast Nidhog is actually doing something.

Really? Going insane over anger and making everyone else actively dealing with your emotions is much worse than Hraes who isolates himself.

He doesn't actually whine. That implies you got issues and you want someone else to fix it for you.
He clearly doesn't give a f*** anymore.

With good reason too, it's not just that his GF died.
It's that she made him eat her for mortals and dragons to live in peace.
Only for that to fall apart, for him to lose his sister and then for his brother to go insane.
And him giving Nidhogg his eye was his own punishment, like Tiamat.

So yea, Shiva's death was in vain and only lead to Ratatoskr's death.
Nidhogg might as well be dead to him too.

It only really sounds like whining, because all we talk to him about is past tragedies.
But I got the strong impression he didn't care if the mortals all died off or if his brother died (the latter is more obvious).
So he said screw that drama a long time ago. That's what it means to be a neutral party.

Though he was pivotal in what lead to the war, and it would've been nice if he kind of redeemed himself.
But both sides were wrong in this, and he was too involved. Supporting either one would've been wrong, and would probably just cause more blood.
It was much better that it came from an outside party and from a change within Ishgard (Aymeric and Estinien).

Even if you do believe he's just whining, him keeping to himself is still better than Nidhogg who forces everyone to deal with his personal anger issues.
Unlike the emo stereotype, Hraes obviously doesn't want attention.
Nidhogg literally made his sorrow into a genocidal song so that everyone could feel his pain.
Really? GTFO.