EU is non-canon. Lucas allowed a lot of people to play in his sandbox, but they had to take their toys home with them at the end of the day.
Apart from the 25+ Years when they were
And Disney are free too, and will borrow anything they fancy turning Canon.
My point stands regarding a Sith is not necessarily evil not at the start, as in Revenge of the Sith Palpatine tells Anakin the story of his own Master, Darth Plagueis. Palpatine was to every fibre of his being, nothing but hatred & evil, he had no ability to love. Yet his Master was so powerful, that he was able to manipulate midichlorians to keep the beings he cared about from dying. A useless power to Palpatine, a soulless creature like him has nobody to care about. But clearly, Plagueis, even as a Sith did love, and have an ability to care for some.
In theory, the midichlorian ability isn't even a dark power, saving from death is at least morally neutral I would think. Though of course that neutral power could turn a user Dark, if he used it for Dark intent, like keeping enemies alive to allow decades of horrific torture.
Even Force Lightning, is a morally neutral tool, a Jedi using it in defence of others for example isn't going to to wreak horror upon his physical body, he is wielding a tool, for the right reasons. Palpatine for example wrecks his body attacking people like Mace Windu with lightning, because he was using it in an attempt to murder, and channelling his rage, his hatred into the force to boost the ability.
There is very, very little Force Lore that is Canon, and much that went on in the EU wasn't trying to establish a new Force Lore, much of the stuff I talk about is simply the Authors having a good think about what we know from the Movies, and taking inferences and logical leaps. People have noticed for example, that Anakin's eyes don't go yellow until his final battle with Obi Wan in Revenge. Mind you, people keep assuming the Birth of the Sith Darth, Vader is when Palpatine anoints "Dark Knights" him. the Birth imo is the moment he leaves his mums corpse, and activates his lightsaber. (People often write or say "Sith Lord, Darth Vader, or Lord, Darth Vader" but what they are thus saying is Lord, Lord Vader!
You only see him his body begin corruption right at the end, for the final battle with Obi Wan. Because his force abilities, his connection to the Force is now finally being driven by pure hatred, anger, and fear. No corruption such as yellow eyes even when he butchers the Younglings at the Jedi Temple, because as monstrous as it was, it was conventionally monstrous, he did not corrupt and misuse the Force to kill them, he did not even kill them out of hate or anger, he was doing a job, one vital he believes to protect the Galaxy and bring peace and safety, and he uses a non force tool to do it, his Saber. Had he been choking, or firing force lightning to murder them would have corrupted him physically.
I imagine it is one of the main reasons that Luke is hiding in Force Awakens, apart from feeling crushed, and in emotional pain and trauma at the butchery of Ren, and of losing his Nephew under his Guardianship and tutorage, had he stayed, he would be expected by the entire New Republic, including and especially his Sister and Brother in Law to go, and face Ren, and try to bring him home. And Luke knows there would be a battle, he is not going to turn up, look mournful, raise his hand out and give "please, Nephew, come home, we can get over this" a try, if Luke goes and faces him, his Nephew is going to come home either in a bacta tank, or a coffin, and with either result, it is not going to be Luke Skywalker going home, it is going to be a corrupted and fallen Jedi. Because just like with Jacen Solo/Darth Caedus in the EU, Luke IS going to have to fight his Nephew who isn't going to just wag his tail and follow his former Master home and Luke will be facing him in Anger, there's no way he could not, the Dark being he faces has destroyed everything he worked for, has presumably killed, perhaps potentially dozens of Jedi recruits, possibly even children. Obi Wan is bloody lucky his final fight with Anakin didn't turn him, but I suspect his love for the boy he was who pretty much, Jedi Master or not, is a son to him was much stronger than his hatred of the Sith he then had to fight.
It is interesting and perhaps notable I think that Kylo Ren is not showing any sign of physical corruption, so I think my theories hold out
he has killed, but conventionally with his Saber, he hasn't channelled negative feelings into abusing the Force to use the twisted powers the use of which would leave a physical mark. Plus, the whole being tormented because he keeps feeling the mighty pull of "the light" stuff, at the moment, he IS saveable. I personally think that if we are going to see Luke dying in the new movies, it will be facing Ren, but refusing to fight him so he can't do anything to him out of anger.
I don't actually think the Supreme Leader is a Sith to be honest, unless Kylo is a name Ren has adopted for himself, it is an odd title to be granted, equally, I don't think the Arrogance and Ego of a Sith Lord would allow Snoke to give himself such a lowly title as "Supreme Leader" It sounds almost like the Imperial "Warlords" with delusions we got in the early EU, when the New Republic has taken Coruscant, and the Empire begins fragmenting through Civil War, power plays, backstabbing, and various Moffs, and Admirals begin going into business for themselves, and rebranding themselves with Lofty titles like "Grand Supreme Admiral" and "Supreme Moff" all the usual stuff little grey men who were often minor, barely competent civil servants or Captains of patrol vessels, out in the middle of nowhere who's reputation was "well, won't actually crash a ship he is Captaining... .probably" like to call themselves.
Apart of course for Grand Admiral Thrawn who was a genuine military genius and commander.
I have always wondered how he knew the Vong were coming though. Weirdly the Star Wars Wiki, though I haven't checked what Wookiepedia has to say as thats the prime best go to resource normally, states that the Vong originated in another Galaxy, but they didn't, their race began on Zonama Sekot, a planet, (Zonama) which had somehow developed a sentient intelligence (Sekot) which was iirc somewhere in the Uncharted Regions, thus in the prime SW Galaxy.