I see where you're coming from, but anyone other than those three appearing to Luke just makes no sense. His two mentors, and the father he just saved but barely knew. Which is also why it makes no sense for Hayden to be there because Luke would have no idea who he is. This is all about Luke. Luke's story has come full circle, and now Luke gets to view those who helped him so much one last time before getting to move on. Lucas stating that Anakin is the true main character of Star Wars just takes away so much.