In my mind Luke is another way in which the ST has made up for the problems of the ST. Much like Han (who has next to no depth in ROTJ), the Luke of ROTJ is simply not as interesting as the one in SW and ESB. He basically goes from fucking up big time at the end of one movies to being uber confident and wise at the start of the next. At no point does him turning to the dark side in ROTJ seem like a plausible possibility.
Huh.
Vader toying with Luke about Leia was really eating at his mind, which really sent Luke over the edge there. The only thing that stopped Luke was seeing both Vader’s chopped off hand and his cybernetic hand, realizing that Vader is still a human as just as much as Luke is, even underneath all that machinery; challenging Obi-Wan’s line of, “He’s more machine than man.”