Rich snobby people in Beverly Hills are still Americans though.
Quel'Thalas and Dalaran aren't part of the same nation so, I have no idea what your comparison here is.
Scattered remnants of destroyed cities and kingdoms in the process of dying out does not a unique race make.
Why not? Sounds like a couple of existing playable races as is.
90% were killed during Arthas' march across Lordaeron. 90%+ of those that remained changed their name only and remained allied with Humans. Later, that 90%+ joined the Horde due to being imprisoned and nearly executed by their former Human allies.
This is incorrect. 90% of the Thalassian population of Quel'Thalas was wiped out by Arthas during his attack on it. Here is a source for you:
https://worldofwarcraft.com/en-us/game/races/blood-elf"Led by the death knight Arthas, a Scourge army stormed into QuelâThalas, slaughtering almost ninety percent of the kingdomâs population."
This figure does not, nor has it ever, accounted for High Elves living elsewhere in the world. Likewise, Chronicles Volume 3 states that Dalaran evacuated it's civilian population prior to the attack by the Scourge, meaning a sizable portion of it's High Elves survived. This population did not return to Dalaran until after the events of Garithos, when the dome was created and the reconstruction of the city began.
During this time we saw High Elves in other locations such as Theramore, Stormwind, and scattered lodges, as well as High Elves from the Alliance Expedition who bolstered the numbers of the Alliance High Elves after the Dark Portal was opened.
In short the number of High Elves is not well defined at this point in time. If the population in Dalaran during the Third War were even equal to 10% of the population in Quel'Thalas, then there would potentially be as many High Elves alive, today, in the Alliance, as there are Blood Elves. It'd certainly explain the strong presence High Elves continue to have in Alliance content.
Let's take this a step further for fun, shall we?
https://wow.gamepedia.com/Kael%27thas
"Kael'thas, together with 15% of the blood elven people, made the journey into Outland with his new allies."
So Kael'thas' army would've been about 1.5% of the original Thalassian population pre-Third War. Now, keeping in mind attrition through various campaigns from the moment he left Quel'Thalas to the moment we see his forces in BC, the fact we saw Blood Elves all over Outland is pretty telling. This is further compounded with excerpts from the Journal of Archmage Vargoth.
https://wow.gamepedia.com/Excerpts_from_the_Journal_of_Archmage_Vargoth
"Entry 1969) <This page is hastily scribbled, in stark contrast to the perfect calligraphy of the earlier entries.>
We've been attacked... Kael'thas' army... thousands of them!!"
So even if, by some miracle, all of Kael'thas 15% survived through the campaigns against the Scourge, the campaigns on Outland, and then the failed campaign in Northrend (and this may or may not even include the loss of the Scryers which was described as the single greatest loss of manpower Kael'thas ever suffered), we see 15% as, "Thousands," of elves.
So when we hear about the 10% of the survivors who went back to being High Elves when the mana draining techniques were delivered to Quel'Thalas, and were exiled, that number could be anywhere from about, 1,500 elves to 2,000 or more.
That's just Blood Elves who went back to being High Elves, and ended up in Quel'Lithien Lodge.
Imagine the High Elves who had an undefined population outside of Quel'Thalas at the time it was attacked by the Scourge.
Long story short, the number of High Elves is undefined, as is their cultural differences. Personally I'm entirely in favor of the High Elves becoming an Alliance Allied Race and bringing Dalaran into the Alliance once and for all in the process.