There really wouldn't have been much to do in Suramar if the Nightfallen had stayed Nightfallen. The arcan'dor and Nightwell wouldn't have been options in that case, so they all would have Withered, and the lore makes it abundantly clear from the start that no one can return from becoming Withered. Take that away, and it also takes away the entire purpose of characters like Runas in Azsuna - or the Nightfallen in general.
In the end, not only do I prefer the look of Nightborne, but I also prefer the idea that they have to survive without the Nightwell (thus, changing their entire culture - no more arcwine/mana juice). They also have no shield anymore, meaning they have to interact with the world now, and they have to atone for the wrongs of their own people. I find it more compelling than "We're addicted, and we
look like a Horde race, so what choice do we have?"
Except, the Nightborne don't have the same silhouette. They stand with their feet wider apart, their torso turned at a three-quarters angle, and their arms are also set wider than regular night elves to compensate for their legs being apart as well. They also have different ears - Nightborne ears curve upward, compared to the flat/straight night elf ears.
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Suramar models
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New models
Compare that to
Shandris and
Jarod, who stand with their feet and hands closer. Night Elves also face their head, chest, and hips in the same direction when idle. They have similar faces (I noticed the males have a slightly different nose shape), but it's hard to tell without seeing more of their faces without helmets on.