This is an interesting (and true) comment - the blood elves aren’t exactly blood elves anymore. Not in the sense players had in The Frozen Throne/early Burning Crusade.
In that case, perhaps part of what holds the Horde together is the shared experience now. Lor’themar, Liadrin, Halduron, etc. - they’ve all been members of the Horde for a decent period of time now. In addition to the qualities mentioned by the OP, part of what holds the Horde could be loyalty and precedent, at this point.
There is no universal concept that would define the Horde in its entirety. This current Horde is too heterogeneous and diverse.
Outcasts? The Nightborne and the Blood Elves certainly aren’t outcasts, and neither are the Highmountain Tauren.
Morals? Nearly every Horde race has its own idea of what is moral and what is not.
Love for war and battle, aka Lok’tar Ogar? The Forsaken and the elves do not share that mindset one bit.
Culture? What similarities do the elven cultures have with the rest of the Horde? Forsaken with anyone else? Kalimdor Horde? They are as different as they can be.
The only thing I would consider they all share in common is the wish to be independent and to be allowed to exist, though that is neither something unique to the Horde nor does the Horde need to exist for that. The Alliance certainly are not forcing anyone to join them or accept their ways. They are not some sort of conquistadors who terrorize and forcibly convert other races (The Lightbound are not part of the Alliance, so no, they do not count).
Blood Elves actually have a lot more things in common with the Kalimdor races of the Horde than the Forsaken who are just former Humans…
with the Orcs they have in common the fel taint, and the fact that their former leader(s) was corrupted by Kil’Jaeden and greatly suffered because of the Burning Legion…
with the Tauren they have in common the reverence over the Light (now that the Blood Elves have the Holy Sunwell and are kinda changed from the times of TBC) and the concept of the “Eternal Sun” who guide them in their culture (the Blood Elves call it Belore)
and with the Trolls they have in common…well their common ancestry since Elves are mutated Trolls, it’s bit like a soldier of modern Italy today fighting alongside a soldier of the old Roman Empire of 2000 years ago
So what they have in common is their past misfortune. That is a valid example. They share that with the Forsaken as well though, since both were victims of the Scourge which was created by the will of Kil’jaeden.
The Tauren do not revere the Light. They revere An’she, who is but one aspect of the Earthmother. In both cultural and religious sense, these two races have nothing in common. They happen to revere the sun, but the way and the reason they do it could not be more different.
Would their shared ancestry mean anything to them however? The elves and the trolls parted ways more than 12000 years ago. They are still two completely distinct and different people with nothing in common besides that. The blood elves waged war with the Amani for several millennia despite sharing common ancestry.
It would mean something to individuals who want it to. Some people are excited to meet family members they find through DNA tests and visit them in the old country; other people aren’t. Maybe the Sin’dorei are excited to meet their foreign, slightly weird distant relatives who eat weird food and ask nosy questions?
I suppose that is possible. Though knowing what blood elves are like, I personally doubt that many would express such an interest. Especially since the Darkspear are rather savage and tribal compared to them.
How dare you?!?! The Sindorei were slaughtered and then betrayed by their prince, addicted to magic and finally Saved and redeemed and restoring the Sunwell. They are not Heroic or anything (need I remind you like 80% of sneaky operators the Alliance kills in their war campaign are belfs? Plus that mage in Baine rescue).
They are fierce and pissed off!
They are just the only Horde race that saw the Light at the end of the Tunnel is all, the still had a harsh path reaching that. And , properly, used that knowledge to assist the Horde in the right direction as Lorthemar supported the voice of reason.
As far as Horde values, one word : OUTCASTS
Rejected by society banding together for survival. Survival and War build a bond stronger than politics and bbq, so yeah, thats what binds us! Cause otherwise we cant stand each other much… I mean we have an entire city made of Gold! These other trolls live in Huts. HUTS!
Ever since WC3, the Horde was a place for those who had nowhere else to go because they were hunted, hated or otherwise threatened.
Most races of the Horde were monstrous and therefore misunderstood as dangerous, or in the case of orcs, still haunted by mistakes of the past.
When the tauren joined the Horde in WC3, they were forced to leave their homes by centaurs and were nomad, forced to wander the land in search of a new home…
Lore Wise Druids are more like an extra faction that accpet everyone who is willing to protect nature.
Just because Druids shared the same space peacefully doesnt mean the races they belonged to didnt hate each other overall.
The Tauren were constantly hunted by the Centaur and living as nomads. Prefering to relocate instead of fight, when they could avoid it. This changed when Thrall used the Orcs and Trolls and together with Tauren destroyed the Centaur and for the first time in Tauren History they creates Thunder Bluff, a city they wouldnt have to relocate from. So they were nomads, living alone, who were finally Nomads no more.
Nightborne were addicts as Belfs, withered (Belfs equivalent was Wretched if you have done the questing) and left to their own fate if it wasnt for the heroes who saved them. Tyrande outside Suramar mocks you when you click her saying “I didnt expect to find you in my birth city helping a bunch of Mana addicts!” So yeah, mana addicts is what she saw, but we saw them for what they were, and what they could be. And they joined the Horde.
Highmountain Tauren and Zandalari are not outcasts, but rather “secluded” or “stand-alone” races. The Highmountain probably because they never had to face any serious foe and didnt really venture alot outside the world, and the Zandalari because of their endless pride.
Yet they too found their place in the Horde, and re-joined the world.
So what they all have in common is that they stood alone, and now they stand united in the Horde!
Void Elves are a joke of the lore, they were created only because some Alliance players requested playable High Elves. Blood Elves wouldn’t just exile some of their members who followed the traitor Dar’khan, Void Elves would have either been arrested or executed by Rommath. And the Alliance races would have NEVER accepted them, I don’t care for how much goody-two-shoes Anduin is or how much Alleria is considered a heroine in the Alliance, Night Elves and LFD Draenei would never work alongside them, it’s just impossible because of their conflicting values.
Also no, Void Elves are not more badass than the Blood Elves, as Aatsui said above it’s showed Blood Elves still use both blood and fel magic despite Lady Liadrin and the Blood Knight’s influence about the Light, they still have mana bombs, they still will resort to anything at their disposal to protect Quel’thalas and their proud people, while Void Elves immediately after joining the Alliance they accept being insulted by Human characters by saying they shouldn’t stay with them in the Cathedral of Light, then they are confined on their space rock with two tents and they don’t even care the Humans don’t help them building a territory for themselves ON Azeroth. Also if they don’t play a big role now that we have to defeat N’zoth, it means Blizzard considers them just like a waste, really.
Fact is that the Horde started as a outcast faction, but it’s no longer the case since races which were accepted by other started to join their faction, and probably outmatch the outcast races by the number.