The Emperor commanded that Luke finish his father and join the dark side, but the young Jedi refused, opting instead to throw away his lightsaber. Enraged at this denial, the Emperor shot Force lightning into Luke, torturing him. Vader rose, the good in him awakened by his son's compassion, and destroyed the Emperor.
Luke believed there was still good in his father, that the Emperor had not driven it from him fully. He tried to convert Vader to the light side, but the Dark Lord claimed it was too late. Instead, he brought Luke before the Emperor on the Death Star.
It was the fact that Luke was his son that caused turmoil within Vader. It was his love for his son that caused his loyalty to Palpatine and the Dark Side to falter. If Vader didn't know who Luke was he would have been just another force sensitive person to be trained to serve Palpatine like an Inquisitor or be killed.
Granted, Palpatine told Vader that he wanted Luke to join them as a dark side ally. But in actuality, he wanted Luke to take Vader's place. Luckily, Palpatine underestimated Luke's growth as a Jedi, which led to his own demise.
Since Anakin's defeat on Mustafar, he needed frequent visits to his bacta tank to survive, and even the Vader suit itself was crude enough for Palpatine to control him. So with an aged body, a mind out of balance and the surprise of Luke's attack, Vader was caught at his weakest point.
Luke and Darth Vader BATTLE Within The Dark Side | Star Wars Canon
Why did Vader stop Luke from killing Palpatine?
Vader's redemption in Return of the Jedi was not just about saving his son; it was also a defiance of the dark side's corruption and his own past as a Sith Lord. Vader's decision to block Luke from killing Palpatine was motivated by his knowledge that it would corrupt Luke and lead him down a similar path of suffering.
While Vader may be stronger, Luke had several advantages of his own. He was both swifter and nimbler than Vader. But the biggest edge was that Luke didn't give in to his hatred and anger.
Ricocheted away from the Death Star and spun out of control, Vader was unable to stop Luke. The space station was destroyed, but Vader survived, and he flew into the far reaches of space. After the destruction of the Death Star, Darth Vader became obsessed with finding Luke Skywalker.
Vader saved Luke by killing Palpatine, but was mortally wounded in the process. Before dying, Vader shared a final moment of reconciliation with his son. As Luke and his friends celebrated the end of the Empire, Anakin returned as a Force spirit to watch over them.
Darth Vader didn't learn he had a daughter until Return of the Jedi, when he stood before Emperor Palpatine. The Emperor's power probed Luke's mind, attempting to goad him to fall to the dark side, and he discovered Leia's existence. "Sister," the Emperor taunted.
She finds it easy to accept Luke as her brother, but she is horrified by the idea Darth Vader was her father. Leia couldn't even understand why Luke accepted it so easily, and somehow believed there was good in their father.
It's less of a question of actual age, rather it's the maturity. Anakin was already highly developed and attached in comparison to other younglings. Not to mention that it's going based off two different leaderships. Luke's own training started late and he didn't follow all the Jedi rules to the T.
Did Darth Vader actually want to rule the empire with Luke or did he only care about finally killing the emperor? Yes, Vader's offer to Luke was genuine. If Vader wanted to kill the Emperor, he would have tried to recruit just any random schmoe to help him do it.
Vader was far more powerful than Luke and easily could have bested him. So, knowing that Vader wasn't allowed to kill Luke drastically changes the equation. His only goal was to make Luke mad, and he definitely accomplished that task.
During the battle, Anakin, who had been known as the Sith Lord Darth Vader, was redeemed by Luke and brought balance to the Force. However, the redemption cost Anakin his life, having been mortally wounded by the Emperor, Darth Sidious, while killing his former Master. After his death, Anakin became one with the Force.
Although her midi-chlorian count is never mentioned, it is clear that Rey's potential is vast. While Vader has peaked in his Force-prowess, Rey is only getting started. Even if Vader is currently more skilled, Rey definitely has more raw power.
Summary. Darth Vader and Kylo Ren are powerful villains in Star Wars, but Vader's control and training give him the edge over Kylo Ren. Kylo Ren may have raw Force power, but Vader's mastery of the Force and lightsaber skills make him the more formidable opponent.
Admittedly, Rey skills couldn't possibly be as developed as Anakin's or Luke's. Nevertheless, considering how fast of a learner she is, and how unique the powers she possesses are, it's not a stretch to say that Rey could be a more powerful Jedi than Anakin and Luke Skywalker.
The novel explained that, had Vader killed Obi-Wan on Mustafar, he would have tried to kill Palpatine too, but given how badly wounded he was after the duel, his power wasn't the same and he was weak, both physically and mentally.
According to series creator George Lucas, the power loss resulting from Anakin's injuries is what drove Palpatine to decide to replace his apprentice with Luke. "Anakin, as Skywalker, as a human being, was going to be extremely powerful,"Lucas explained in 2005.
