I would say they are arrogant, but I think they are on verge of even greater change that should see them more ambitious and determined to now embrace new things or former old things that were good but they felt they had to leave behind because of the "complications" they caused.
I think Tyrande is still annoyed at the WotA events, why? Because these are more than just any other people to her, afterall they behaved far better than the shen'dralar did in the wotA, but Tyrande seems almost cross in a way you would with close family, judging them by higher standards than you would a stranger.
There's history there, and I think it would be disappointing if blizzard instead chooses Tyrande to maintain the whole "nightwell must be destroyed" rather than cleansed stance, which is fine to have in the initial reaction because you're a bit emotional, etc, you don't know what's happened. but once you have discovered the courage the nightborne are showing, also heard their side of the events and seen they're actually as committed to disposing of the legion and Elisande in a similar way to how Ravencrest and Farondis rose up against Azshara, as well as the other night elves - coupled with the fact that her side is desperately in need of the magical boost, it's like their biggest deficiency, add to that the result of destroying the first well - it would be insane for Tyrande to seriously want to go through with destroying the nightwell.
3 other factors also have to come into play too.
- 1. The cure. The nightborne are cured of the enslavement of the nightwell, and consequently all highborne, night elf kind have freedom from arcane imbalance (addiction) that started before the war of the ancients. This is the long work of the Valewalkers. Tyrande at the point of the statement doesn't know this. The use of magic or nightwell will no longer be a health hazard - as the arcane should never be. The source is still corrupted, but that is something priests can fix. they've been cleansing moonwells all this time.
- 2. The nightwell is not the reason for the demons' arrival. Tyrande doesn't know that yet. She isn't aware of World souls, at the time of this, khadgar only just found out after Magni's revelation a little earlier. As far Tyrande is concerned, the demons are after the well and it's Night elf well's that keep drawing them. She isn't even aware that the Well is life blood of the planet -all those leylines the eye of aman'thul combined with the small font atop suramar palace to form the night well are Azeroth's veins and arteries. She isn't aware of this yet. Which might be why despite the gains using a well might have, she at that point thinks it shoudl be destroyed.
- 3. Illidan's return will change things again, because the whole "vexation with the well of eternity" stems from his presumed betrayal in setting up the well of eternity and the misconception that it is all the demons are after. Remember Tyrande and the night elves still think this is the case. It is Illidan that will provide the truth on this, and Elune is behind him, this will be significant for Tyrande. Who's always been coming to his rescue. She did it on top of Hyjal by persuading Jarod not to sentence him to death, and she freed him, killing members of her own order who refused to obey her - because it was important. She again advises her husband that they need the Illidari demon hunters at Anduin's coronation after the Broken Shore when the Slayer reveals the demons in the throne room.
Illidan will want to use the potential of the Nightwell to strike at Argus. remember that his spell in the novel Illidan needed a powerful source, the WEll of Eternity would have been perfect, except he had no access in Outland, and now he would want to use the Nightwell. furthermore, the arcane source with magic been wielded can be used for a hell of a lot more than the night elves were using it for, not just healing the land and enhancing natural life, but rebuilding their broken civilizatoin.
You'd have to factor in there will be a shift in night elf psychology and motivation after this - Suramar returned is a full functioning majestic city from the past, though forever lost, but it gives a building block. Illidan's revelation about the demons, the titan soul, Azeroth - a lot of night elf guilt would perish and it would be replaced with a drive to rebuild and be able to take the fight to the demons. Tyrande as a tactician would know quite well the druidic powers and priestly powers will not be sufficient, They were not sufficient against deathwing, the twilight cult, the horde or ragnaros, they needed the arcane, like they needed it in WC3, and they can't be relying on humans to provide it for them when they have far better and more skilled masters in their own racial group in the nightborne and highborne, there own kin. As cross as she may be initially with them, Tyrande will have family and friends amongst the nightborne, and we see her wanting to help them.
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it's more like they know it annoys the night elves especially than anything else, it's like when white racists tend to call blacks monkeys, and blacks are offended by it, even though most of the insulters know we were all black once and all came from monkeys. And yeah, how many women call men hairy apes, caveman or monkey, yet the white ones don't seem anywhere near as offended as the more senstive black ones. Especially in britain and the U.S - and the reason this is because of this over-sensitivity black westerners have over racial references to them by whites... something that is not shared by african blacks who couldn't care less if they were called monkeys or not.
Classic school psychology, you call people the names you know irritate them the most. No logic needed, the goal here is to insult, provoke and spite beacuse of your hatred or dislike, so you use what they're most sensitive about.