Weren’t the Highborne kicked out from the Society of the Kaldorei?
The Kaldorei belongs to the trees. ( the leaf customizations prove it)
The Highborne are us the, the society that was kicked out from the society of the Kaldorei.
Back in Cata the Highborne did not had their own model. For example, Zandalari, they were hunched back like darkspear trolls. But they got new model. ( so you cannot say Highborne are nightelves of Kaldorei)
Highborne got its new model.
You want to be a Highborne ? The Horde is waiting for you.
Just deal with it.