Bottom line, Dooku never considered himself a Sith. And he wasn't; he was a man looking to change the galaxy in a way the Jedi were unwilling to try. And that is why he joined the Sith and became Darth Sidious' apprentice, Darth Tyrannus. When Dooku became Sidious's apprentice, he was already an elderly man.
The reason Dooku joined the Separatists, he said, was that he learned a terrible truth: a Sith Lord called Darth Sidious controlled the Senate. With Obi-Wan at his side, they could destroy the Sith. “I'll never join you, Dooku,” the Jedi said.
Like many of the other Sith, Count Dooku was incredibly proficient with the Force, even being able to win a fight against Yoda. Despite this, though, he still wasn't the best fighter with a lightsaber, and his Force skills were not nearly as powerful as Darth Vader's.
Kylo Ren did not have a “Darth” name because he wasn't a Sith. “Darth” is a title given to Sith Lords of the Sith Order. Kylo used the Dark Side of the Force, but he wasn't a member of the Sith Order.
He fell under the influence of Supreme Chancellor Palpatine of Naboo, and left the Jedi Order. After learning that Palpatine was secretly the Sith Lord Darth Sidious, Dooku turned to the dark side and became a Dark Lord of the Sith himself, replacing Darth Maul as Sidious's second apprentice.
His best friend had been given a gift that could have allowed the Jedi to help countless people, but Yoda refused to act. As a Jedi, Dooku couldn't stand the thought that his best friend was suffering without a purpose, so he hated Yoda and the Jedi Order for that. In the end, though, Yoda was right.
In canon, we have seen Sith having yellow eyes for two reasons: they have complete and total dominance over the Dark Side of the force (I.e Emperor Palpatine). Dooku did not by any extent have a mastery over the Dark Side.
Rey didn't become a Sith Lord imbued with the soul of Palpatine because she didn't kill him, he ultimately killed himself. His greed, recklessness, and thirst for power were his undoing. Star Wars: The Rise of Skywalker is currently in theaters.
1 Darth Sidious
There has been no Sith, as powerful, meticulous, nor as evil as the Emperor himself, Darth Sidious. As previously mentioned, Sidious trained in the Dark Side by Darth Plagueis before Sidious killed Plagueis in his sleep, making Sidious a Sith Master.
Put simply, “Darth” is the title that precedes a Sith Lord's name, and roughly translates to “Dark Lord.” The term was used by the ancient Sith, and preserved by Darth Bane, a Sith Lord who survived the Jedi-Sith War. He was the one who passed down the ways of the Sith to more “modern” Sith masters.
More than a strategic retreat, Count Dooku running away from Yoda is a reminder that Dooku is far less powerful than Yoda. Dooku could have not beaten Yoda in Geonosis, meaning that the fight would have ended with Dooku either killed or captured had it continued.
Revenge of the Sith (2005)
Anakin gives in to his hatred of Dooku and uses his anger to overpower him, severing both of Dooku's hands and leaving him helpless.
In legends, Dooku actually explains why he hates Anakin: He could feel Yoda's touch still lingering on the edges like a distant echo. Vividly his mind went back to their last meeting, on Geonosis: swords drawn at last, and finally equal.
Studying Jedi Archive records, Dooku based his new weapon design after the curved hilts that were standard during the heyday of Form II lightsaber combat. The curve allowed the hilt to fit better into his hand, allowing for superior finesse and precise blade control.
N'Kata Del Gormo was a Force-sensitive male Hysalrian Jedi Master who lived during the times of the Galactic Republic. According to legend, he found and trained Yoda and a Force-sensitive Human friend.
When Dooku left the Jedi Order to become a Sith Lord, Yoda thought he merely left rather than turned to the Dark Side. Dark side clouded jedi orders ability to sense things properly. Also yoda did not believe dooku was a Sith lord.
killed by an Imperial strike team, his dark side, like many Seth before him, refused to let go of life.
Master Yoda has risen above all others to claim the top spot as the most powerful Jedi of all time and the true chosen one according to IGN's audience. He won pretty handily as well, as he was victorious in 89,756 of his 95,243 battles and had a win percentage of 94.2%.
Truly, the most powerful Sith Lord was Darth Sidious, better known in his public persona of Chancellor (later Emperor) Palpatine. Through cunning and manipulation, Sidious killed his master to claim the mantle of Dark Lord of the Sith.
He transforms the Galactic Republic into the Empire and declares himself Emperor, using Machiavellian manipulation to invoke martial law. Palpatine rules the galaxy for over two decades before Vader betrays and kills him to save his son, Luke Skywalker.
In The Rise of Skywalker's novelization, we learn that Rey's father was a failed clone of Emperor Palpatine. He was initially created to be a vessel to house Palpatine and his Sith power.
A dark side warrior with a mysterious past, Kylo Ren was neither Jedi nor Sith, but a product of both sides' teachings. Once an apprentice of Luke Skywalker's, he killed his fellow students and drove Skywalker into exile, becoming a First Order warlord and servant of Supreme Leader Snoke.
“The tear [on Anakin's face] says that he knows what he's done, but he has now committed himself to a path that he may not agree with… but he is going to go on anyway. It's the one moment that says he's self-aware that he's rationalizing all his behavior.
Though one thing is for certain: Kylo Ren/Ben Solo does not have yellow eyes because he's not "corrupted" by the Dark Side.
While Jedi could create Force lightning, like Sith, they choose not to use that power due to its association with the dark side and immoral nature. Despite being equally as strong in the Force, one innately Sith ability that Jedi in the Star Wars franchise do not wield is Force lightning.