It's more healing intensive than other NM trials, sure, but if your healers are really struggling that much then I'd say there's also a problem with the tanks' CD usage. I tanked Nidhogg NM on my i205 WAR and, sure, it hurts a bit sometimes - but popping the right cooldowns at somewhat-right times makes it very manageable.
I feel like this fight is just the right difficulty at the moment - it's hard enough that it feels like you're fighting "vengeance incarnate" and that you're ending a war, but mechanically simple enough that it's easy to learn the fight.