Anakin already murdered a whole village out of “anger” in AOTC. So killing one extra guy is nothing. It’s not a turning point or a good example of characterisation. Is Dooku more human than the sand people and therefore a darker step along the path? Does Anakin even learn anything new about himself or the dark side? We may never know. There’s no apparent easier path, or any obvious seductive power.
Luke at least used dark powers to allow his easy access to Jabba’s palace, and fell afoul of his abuse of the Jedi mind trick. When he lashes out at Palpatine it’s the same, his temper does more harm than good. Then at the end with Vader it’s clear the strength he gains allows him to win the fight. But instead of seeing this as a great advantage he’s the better man and corrects these mistakes. If he was weaker he might have let the victory influence him in a different way, that’s why these moments in ROTJ work.
Vader’s redemption is certainly iffy, but in the context of acting selflessly instead of selfishly it’s enough. As long as you ignore his supposed child murdering days. In a broader sense he’s finally giving up all that power to remember his humanity. It’s less about killing one last bad guy and more about the sacrifice.