And Luke says he has only seen one person more powerful than her; that means it is, in order, Kylo, Rey, Emperor Palpatine, Anakin Skywalker, Obi-wan Kenobi.
And this where i, again, have significant issues with the newer movies and the continuity between the originals. Also, your list is completety wrong and omits a huge, key character.
Vader was, without question, the most powerful “force user” in the star wars galaxy. He was not introduced as such in a new hope but was back storied as such as the movies went along. Vader was far more powerful (that is to say innately talented) than palpatine prior to being crippled on mustafar.
Anikin was vergance in force. Literally an immaculate conception. That was why palpatine wanted him so badly to begin with. That was the whole (clumsily told) plot line of the second three prequals: the battle for anikins soul. The most powerful being in the galaxy being corrupted.
So your list is flawed from the start. Vader is one and its not even close. The list then omits a huge key player in yoda while missing the plot line being followed in the first two movies, that of older martial arts masters taking on singularly gifted students.
Palpatine wasnt “stronger” than yoda nor was yoda “stronger” than palpatine. They are two sides of the same coin, yin and yang, meant to be a balance. The younger yoda lost, as was covered (clumsily) in many ways, because he lost focus on the true nature of things. He lost his balance. Palpatine never cared who won or lost the clone wars. It was irrelevant. He simply wanted to draw the jedi into a conflict they should have never have been in in the first place. He unbalanced them from the light and let them cause their own downfall. That, however, doesn't negate yodas innate strength and mastery of the force. He was palpatines equal all day every day, being the other side of the coin, as it were.
So the list, according to the world lucas made, was vader one, palpatine and yoda sharing a second place as wizened old masters samurai/ninja, followed by their respective students. Luke was so valuable to both sides simply because, as the offspring of someone who was born as a vergance in the force, he would have inherited considerable potential. It is flawed and, once again inconsistent with the established thread of the series, to make kylo (two generations removed) stronger than either his mother (who had never shown more than basic force potential) and had a nonforce sensitive father, and stronger than his grandfather who was the original source of the power, being the result of a vergence in the force.
Again, dont be mad at me for understanding and following along with the plot lines that were established and then, when you try to rewrite them after fact, i call bullshit.
If lucas and disney want to rewrite the starwars universe thats their privilege to do so, and its mine to point out the obvious inconsistencies and lazy slip shod writing.