Bingowings:
Besides most of the problems in the Star Wars galaxy were not caused by Vader or Palpatine (they just exploited the mess that was already there).
But that has nothing to do with what these movies are about. The original trilogy, with the prequels now heavy-handedly underlining it, is absolutely nothing to do with that; they are about making the right choice, doing what is best for all and not for one, and believing in yourself (before one's level of metaphorical self-belief could be quantified by a blood test!).
Anything else, like a third trilogy, would feel like an extension, not the final part of the whole. There is a distinct and intentional story arc to these six movies, and it's complete.