Another thing re-watching the original movies has reminded me is how stupid the (apparent) setup for the new movies is.
In Star Wars, Vader is a medium-level commander at best. He might be in charge of the ships that get Leia, but once he meets up with the other imperials he's clearly subordinate to Tarkin and a peer to a dozen other commanders, some of which are openly contemptuous toward him.
In Empire Strikes Back, Vader's apparently been put in charge, and, again, his immediate subordinates treat him with contempt. After he murders a couple of them, they stop questioning him because they're afraid. But clearly they don't like him and are seen making comments behind his back. Then in Return of the Jedi, Vader again just intimidates people. No one seems to like him, and no one lifts a finger to help after he's hurt. They just give him a wide berth. And of course the end result of Vader's leadership is a calamity.
Nothing in the original movies gives the slightest hint that anyone who was left would be receptive to another Vader.