Vader’s redemption is pretty bad honestly and comes out of nowhere. Kylo’s redemption has at least been 3 whole movies in the making. The specific moment with Leia is not handled very well but otherwise this is definitely something they’ve improved upon (though there isn’t anything that touches the moment when Vader turns).
The problem for me is, that TLJ to a large degree was about Kylo’s potential redemption, and in the end he chose to become the Supreme Leader. For me TROS didn’t provide a compelling reason to backtrack on that significant development of his character, and it thus feels unearned for me, despite Adam Driver’s good acting. At the end of TLJ Kylo Ren becomes the Emperor, while in TROS he is quite clumsily forced into the Darth Vader role again right down to the mask. For me TESB was always in part about Vader obsessively searching for his son, indicating that his priorities had shifted. Having failed to convert his son, Vader sort of came across as a broken man in ROTJ, resigned to his fate to be replaced by his son (it is too late for me son). Luke gave him an alternative path, that he only took when he was forced to choose between serving a master, who would replace him, or his son.
I feel urge to to argue TLJ with you for the nth time, I’ll just say that’s not my read of him in the film.
ROTJ is, in my mind, the same sort of character fumble for Vader as TROS is for Kylo in the first half.