Luke defeating the Knights of Ren accurately shows why Ben would defeat them so effortlessly later on. Only one Knight, Ren, has a lightsaber and the rest have customized but regular weapons. While they are tapped into the Dark Side, they are not trained in it and as Luke puts it they use it "like a hammer". Luke uses the Force and his lightsaber to completely beat them. The same thing happens for Ben. While the Knights initially have the upper-hand, it is only when Ben does not have his lightsaber. Once he gets it from Rey, he curb-stomps them. They are still untrained Dark Side adepts and are no match for a fully trained Force wielder.
Ben is telepathically communicating with Snoke when still a child. He also communicates with Ren telepathically. After The Rise of Skywalker, it is revealed all the voices Ben heard were really Palpatine the entire time. Palpatine was corrupting him from the beginning.
