Well why the hell did Vader deserve redemption? At least Kylo had layers, some obvious conflict. The great thing about the TROS version is that Kylo’s redemption was a by-product of what was going on. Rey was on mission (both in the DS wreckage and on Exegol) and Kylo’s turn around came about as a consequence of their interactions (and Leia’s death) - not just a matter of Rey throwing everything aside to win his heart. Luke’s entire focus on DS II was saving Vader when he should have been fighting the Sith with every last breath. The idea that Luke became some kind of legend for this is absurd to me. So I absolutely prefer Kylo’s redemption over the cockamamie “Vader was really just a nice dad and you should always support your dad” thing of ROTJ.
I’ve never seen someone who hates Vader’s redemption before, so this take seems really bizarre to me. If you don’t think Vader had any conflict in the OT, did you even watch those movies? Throughout the trilogy, Vader just seems tired of being the Emperor’s lapdog. When he finds out his son is alive, that becomes his only focus. He was already in a position to be redeemed by Luke, he just needed the push of seeing the Emperor torturing his son. So I don’t think it’s some kind of “support your abusive dad” message, and I feel like the idea that Luke should be religiously focused on fighting the Sith goes against the principles of the saga. The old Jedi were wrong because they were focused on fighting the Sith, and they couldn’t see the manipulation occurring right under their noses. Luke managed to see through the darkness and redeem his father, ending the Sith once and for all.
There was nothing pre-ROTJ to indicate Vader was a conflicted soul. This is primarily because he wasn’t - Lucas hadn’t written him to be the fallen Anakin Skywalker until very late in the process. So ignoring his actions from within the Empire let’s consider Vader from Luke’s perspective - Vader’s dogged pursuit of the DS plans led to the grisly death of Uncle Owen and Aunt Beru, he tortured Leia on the DS, he killed Obi Wan right before Luke’s eyes, he shot down Luke’s comrades during the DS battle - one of whom was Luke’s boyhood friend, he tortured Luke’s friends on Bespin just to get a rise out of Luke, he beat the crap out of Luke and offered joint custody of a new fascist Empire, and finally Luke was so horrified that he attempted suicide rather than accept Vader as his dad.
I fail to see how from this we get to Luke’s “there’s still good in him” stance of ROTJ. And don’t get me started on the ethics of remaining calm while countless innocents are being annihilated by a super-laser…
What we see in TESB is the shock of the initial news. What we see in ROTJ is Luke the Jedi who has contemplated and reflected and searched his feelings. Even at the end of TESB, Luke has accepted the news and is wondering why Ben and Yoda didn’t tell him. He asks Yoda in ROTJ, but he knew it already. In TESB Luke was brash. In ROTJ he has gained wisdom from his defeat and gained new insight. In TESB he sought to save his friends from the evil Darth Vader. In ROTJ he sees the path of possible redemption for his father.
And we don’t know when during the development of TESB that Vader became Luke’s father because Lucas never put it in the script. That scene was left unfinished and the reveal was only told to Hammil in person. Prowse said “Ben killed your father” on set. So as far as we know, he came up with that idea early on.
And you have to remember that when we meet Luke, he is obsessed with learning about his father. That is kind of a running theme in the scenes on Tatooine. So if he sensed some conflict in Vader, he would jump on the chance to redeem him and get to know him. But alas he only gets a brief time.