The Zandalari have a far stronger horde loyalty and incentive.. you believe them when they wanna kill the Alliance.. the nightborne.. you are half like.. why are they even here or fighting, and the other half of the time you half expect them to be on the other side.
They are the only horde race I get that with.
Blizzard need to do something to sort their horde identity out. They have to decide what sort of allies they want them to be? The all in type or the periphery type. Maybe the reason they ahve'n't consolidated them in is because they plan to do something with them, but they should hurry up and do it.
I would much rather half the nightborne fully committed to the horde, or even a fraction of them, than this current state of affairs.. they have too many ties to the alliance.
With the blood elves, you have the thalassian vs night elf hate thing going on, this is what partially made the void elves possible on the alliance via the humans, as the high elves have been friendly. Secondly the blood elves have a human hate or distrust established, even phobia thanks to Arthas.. so you can understand that.
The nightborne - well Thalyssra in 7.0 and 7.1 is portrayed as decent person, as is her rebel group - and the story has the nightborne owing their lives, and the surviving of their city to the other Suramar kaldorei who are now in the alliance - and twice over. first in the wota, then again in Legion expansion. Then you do the quest and they have a boner for all thigns kaldorei - I guess cos they identitfy themselves in that vein - which at least the Tahlassian elves don't have - they are everything opposite to the kaldorei in kaldorei are night, they are day, kaldorei stars and moon, they are sun, kaldorei Elune, they are the Light, nightborne still feel very kaldorei - just arcane kaldorei.
Imo, they need to write a story that puts either all the nightborne, or some of the nightborne firmly in the horde either that OR, they go the peace route and write the nightborne as the bridge between the elven people - and use them to do something new.