But Luke wasn’t planning to appear before the Emperor - Vader took Luke to Palpatine when he initially refused to turn back to the light side as Luke asked him to. Luke wanted to surrender to the Imperials to avoid having Vader sense what the Rebels were doing through him, and to have a face-to-face talk with his father. If he failed at turning his father, he might be killed, but his friends would no longer be in danger from his Force link to Vader.
And besides, why would Luke think it was his job to kill the Emperor anyway? The Rebel fleet destroying the Death Star was supposed to be responsible for that.
So now we come full circle and you guys have accidentally made my initial point for me.
This conversation began with me saying that back in '83 it bugged me that Luke did not actually save the galaxy. As you say a) he turned himself in because his being sensed was a liability, b) his only concern was redeeming his father - not destroying the Sith, and c) it was the fleet destroying the DS that was responsible for the victory.
Note there is nothing good about Luke having to turn himself in to nullify detection. This makes him a liability - not an asset! What turned the tide of the battle was Chewbacca hijacking a Scout Walker, not the fact that Luke was in the throne room. The movie should be called Return Of The Wookiee.