CT Palpatine's plan in ROTJ was very weak.

Luke shouldn't have to kill any of them, really. By holding up the Emperor's head, the message is very clear: Surrender or end up like him. The imperials' biggest concern should be whether or not Luke accepts their surrender. Then when Luke demands a favor from them, that’s their opportunity to show their (new) loyalty.

Well as it turned out in the actual movie, the rebels actually managed to win in all battlefields. That scene with Luke dragging Vader was after the destruction of the both the shield generator and the main star destroyer. The imperials on the death star were frantically running around (completely ignoring Luke and Vader), presumably because they knew what danger they were in.
That's not the situation when Vader said that line, "Give yourself to the dark side. It is the only way you can save your friends." The Empire was completely in control at that point. It looked like the rebels were all going to die. So the coup idea makes sense as a last, desperate attempt to prevent that.

 

Death Stars don't blow up planets, they teleport them or Force Transfer them to other times and places, sometimes whole new Universes using the power of The Force to make it look like the planet was destroyed. Often "destroyed" means that the whereabouts of the planet are destroyed, such as with Alderan, a planet that was so peaceful and had no weapons that the Empire had to hide it in time of war, so it needed to be protected and saved by that Death Star that the Emperor had constructed and oversaw the management of. Luke didn't kill anyone on that Death Star either, it also was moved to another place with the power of The Force. Do not underestimate the power of The Force or even the Kyber Crystals Lightsabers and Death Stars are both powered by. Much like Lightsabers which seem to cut but actually cause no pain and re-energize limbs later in-secret or openly, sometimes with robotic limbs but fully there as well Spiritually (you don't have to see things with your eyes for them to be there.) Lightsabers often put people in a deep trance when it seems like they were killed, or transfer them like Force Ghosts move to distant worlds, like Luke and Yoda in Rise of Skywalker, and Luke in IX, The Force can give instant Soul-Travel. Sometimes even to the Spiritual World. No Dark Force power has physically or emotionally hurt anyone. Remember how many times Snoke and Ren would throw people against the ceiling or the wall? They would appear fine just a little later, The Dark side simply asks to stay hidden among its followers, and had been hidden among so many Star Wars fans but all the while it is as beautiful and Loving as the Light Side of The Force, and necessary for saving The Galaxy and dismantling large batallions of troops such as The Empire, The Clone and Droid armies, and The First and Last Order. Without Shiv Palpetine at the command of these Empires and fights there would be evil chaos at rule instead. Palpetine is an Eternal Jedi, and so is Vader. This was and is well known and hidden amongst the Jedi, many of whom back then went into hiding after Order 66, which didn't kill the Jedi, because the blasters were recalibrated to be harmless and to let them know the Order was in place and they needed to pretend they were passed away, for The Jedi to be preserved amidst the new Empire, with the Jedi still protecting The Galaxy from secret locations. Palpetine and Vader did a marvelous thing in stopping a long held war that had a lot to do with greed, and they held fast to the ideal that there must be a balance in The Force, as well as peace in the Galaxy. They sacrificed much.

Neither Death Star was destroyed then, and those Death Star runes are runes that were planted much later by The Force itself. It took many hours of many Jedi using immense Force powers to save both Death Stars when it looked like they were exploding. Like the Force illusion on Dagobah but much more intense. Let the Force flow through you and create Peace with it.

Anyway, try to watch the Jedi films from the point of view that the Force is Love and only Love. Don't give up on Vader or Palpetine, and you might just find out the true meaning behind what a Jedi Knight really is.