Hmmm
Luke did not destroy any kind of sith member, anakin skywalker was the chosen one to end the dark side and balance the force and he did. Anakin skywalker was the one that killed darth sidious when he was zapping luke. All luke was there for was to bring him back from the dark side. all along anakin was always the chosen one. and for the whole luke training in 1 week or so? look at his muscle in ANH, and look at it when hes on degobah, complete difference in muscle tone and everything, now i know this is really the actor working out but lucas was making it look like there was alot mroe time in between movies then what we had see, they could have been on hoth for 5 years and we would never know it. not to mention luke had the 2 best jedi's to teach him and he already had a head start being a skywalker.