In my view, Kylo's redemption arc starts at the end of TLJ when Luke shows him how foolish and useless his anger is, and how truly alone it's made him. It's Luke's final lesson to Ben.
And then in TROS, it's driven by the return of the Emperor which sweeps the rug under his feet and really makes him realize how much of his life has been a lie. Snoke, his grandfather speaking to him. He has a kind of rebirth when Rey stabs him and stops him from dying, and then is finally able to find forgiveness when Leia shows him the memory of his father. Fighting and defeating the Knights of Ren and facing Palpatine is him finally confronting and turning his back on all the manipulation. He dies giving his life for the one person left that he loves. It works for me.
A lot of people misinterpret the ending of TLJ as cementing Ben being evil, when really it's the opposite. He starts the movie kneeling to Snoke. Then he achieves his major goals to gain power - Luke is dead, he kills Snoke, and he's the Supreme Leader. And yet he ends the movie without any satisfaction. Kneeling. The same way he began.
So yes, Colin's version would have been many times worse.
This is just pure nonsense. Colin's script is 100x better since it commits to what TLJ sets up. Bendemption is not impossible after TLJ, but it shatters once and for all the idea that Ben is "tragic." He's not Anakin Skywalker. His fall to the Dark Side was not a tragedy. It's what he wanted. As he states, "I am a monster." The end of TLJ shows that when the chips are down, he willingly chooses power over acceptance and love. Snoke is dead (the person who supposedly manipulated him), Rey is willing to forgive and accept him, his mother wants him back, yet he still chooses to remain Kylo Ren because that's who he really is.
TROS' "redemption" is hollow because at no point does Ben Solo accept that his previous actions were wrong, at no point does he come to understand that his viewpoint was incorrect. He's stabbed by Rey, healed, and then turns back into "good ol' Ben Solo." Vader, in contrast, is able to reflect and accept that he was wrong in ROTJ before dying and redeeming himself. He straight up tells Luke, "you were right about me." In his last moments he understood that all his hatred and pain gained him nothing and nearly cost him the one thing that he started down the path to save in the first place, his family. By reflecting and accepting on his past actions and why they are wrong, he is able to be redeemed.
There is no such reflection and acceptance with Kylo Ren. His father appearing to forgive him is not sufficient given Ben's crimes, it does not correlate with his downfall. To reiterate, Vader fell to the Dark Side primarily in an attempt to save his family. At the end, he was so consumed by the Dark Side he nearly destroyed his family. He's redeemed by remembering why he started down this path to begin with and saves his son, recognizing that the Dark Side only ever led to destruction and pain. Kylo Ren did not fall to the Dark Side because he wanted to save his family or because Han Solo was a bad father. The films show that he willingly chose this path, seduced purely by its power. This is why Han Solo was unsuccessful in convincing him to back down in TFA, Ren wanted power more than family, love, or acceptance.
In order for him to be redeemed he needed to understand what the sole pursuit of power rewards you with. This is why Treverrow's script about him visiting a Sith Tomb and Luke's Ghost reminding him that this is where his path will lead him to is on point. Kylo has to confront why his pursuit of power was wrong, he needs to understand what it ultimately leads to and why it's not something he should desire. Shit,
Rebels does this so easily with the character of Agent Kallus. He starts the series as a perfect Imperial Agent and one to be feared. Eventually we see he has a certain sense of honor and believes in the ideals of the Empire, he doesn't question them. The crucial turning point comes when he and Zeb get stuck on a planet together and end up working together to survive. In the end, they are both saved and return to their respective sides. However, Zeb is returned to greeting friends who embrace him and exclaim how worried they were about him. Kallus returns to the cold empire and a solitary room. No one cares what he's been though. No one embraces him upon return. No one asks him how he's doing. He's just another disposable cog in the Imperial Machine. And, this is what leads to his turn to the Rebel Alliance.
Kylo Ren could have used a similar sort of poignant moment, a reflecting point as he achieves complete mastery of the galaxy only to find he is no more happy than when he was a pupil under Luke. Such a moment could be contrasted with Rey, "the girl from nowhere" whom everyone loves and embraces, even his own mother. Hell, keep the stupid "Rey is a Palpatine" twist in and such a moment could still work as it would show Ren that even though her ancestor is the literal personification of evil, none of her friends care and still embrace and love her, including Leia and Han. Examining and reflecting upon such a moment could lead to Ben finally turning from the Dark.
OR you could have Force Ghost/Memory Han show up to forgive Ren for murdering him and then Kylo immediately switched to the Light...