My vision is to have something like that.
The higher arcane emphasis of the horde elves makes them more powerful but also more vulnerable, less healthy and whole.
The alliance elves have their night elves incl highborne and high elves and void elves but their mark of distinction is a more wholesome approach. Elune and nature magic complimenting night elf arcane users , light magic complimenting high elf arcane uses and void magic enhancing void elf arcane users.
so while the horde elves would have a slight arcane edge there. Is a flip side in the other specialties the alliance consider seriously do make them no less formidable, and from a certain point of view (non gameplay), better. The idea is horde fans would think they are better while alliance fans would think they are.
The roots of both the blood elves and Nightborne don’t forget are principally based on the alliance int he high elves and night elves. That needs to have a reflection with its own advantages and disadvantages.
Obviously there are reasons blood elves and Nightborne moved away from their origin and became what they are, reasons that suits them, but weighing against that is the most successful eras of both elven groups were in the origin groups who exist still and have improved with changes of their own.
Horde fans will see a hope their elves are better for the changes they endured or had to make which time will prove, while alliance fans have the greatness of the past as their proof but also the gradual developments and evolutions they have experienced enhancing them and their original identity they haven’t altered (now do you see why though a Druid NElf fan I am passionate the arcane and presundering side of the Kaldorei continues clearly visible in them. Never said it had dominate like in the Nightborne or even be huge. It just had to be there, clearly visible and part of their package because they are the full picture of the Kaldorei in all their facets.
This should help also add to a different feel and perception while at the same time the similarities should be clear between alliance elves and horde elves.
You want to achieve essentially simultaneously being both very alike yet very different. Even in common areas like magic all elves share.
Emphasis on how they work together will play the largest role in bringing that out.
Highborne work different from Nightborne because of the much heavier Druidic and Elunic influences that promote balance, harmony and humility. This has clear advantages but also means a less prominent arcane focus if that’s what you like. While Druidism and Elunism can and should exist in the Nightborne, the degree is not only far less, but heavily skewed to the arcane elements in Druidism and Elunism which do have a lot. This is one of several areas that illustrates similarity and difference i. A way that is pronounced either way. Here is another.
The entirely urban centric life of the Nightborne is different from the more overall mixed life of the Kaldorei who would have urban centres like a capital for their urban life and rural life in the forests as well as temple life. And the effect is noticeable. Not to mention they are a far bigger group.
Same with blood elves who have a much higher population, broader infrastructure and land mass whereas high elves are refugees and void elves just settiting up. Even if they get a great city they would be more city state like Nightborne than nation state like blood elves and night elves.( or rather what night elves should be! It is biased and unfair to have all alliance elves fringe, marooned and homeless for many reasons incl lore wise given the fact the core of the elves is alliance and the species’ biggest fan and support base sit blue)
So basically, the position is reversed for void/high elves in the end than it is for night elves/Nightborne. Because Blood elves have the city +country and full life picture. High elves and void elves just have the city with a very specific strain or vein of focus.
Same for the night group but in reverse. Night elves have the city and country, while Nightborne just have the city