I guess the reason Vader didn’t kill Kenobi earlier is that he couldn’t bring himself to do it and the reason Kenobi didn’t kill Vader is he couldn’t bring himself to do it. Which is also the reason he didn’t do it in Revenge of the Sith. So really neither of them can bring themselves to kill the other so it’s kind of pointless except for the emotional parts of Obi Wan seeing Anakin as Vader and hearing from his own mouth that Vader “killed” Anakin (which I really liked.)