I think some may have missed some of the setup for Kylo. He was already troubled when Luke started training him. He was already heading down that path. Something in him was seeking and he settled on Vader, his grandfather. For 23 years he held the power of the galaxy in his hands. He was the right hand of the Emperor. He was mythic. Kylo worships him as a hero. To us he is the villain. His path goes along a dark path that culminates in him killing his father. But even doing that doesn’t bring any peace. Instead he kills his teacher, Snoke. That doesn’t bring any peace. Kylo is still conflicted. And Rey is a key player. She can see the conflict. She helps bring out the conflict. Between Rey and Leia, they finally reach him. There is always hope. That has really been a theme of the saga. That there is always hope. Hope in a rebellion, a resistance, hope for a father, hope for a son. It is a timeless message about not giving up on people. Luke doesn’t give up on Vader so why should anyone in the ST give up on Kylo?

And as for Kylo’s acts being less evil than Vader… seriously… the younglings… Vader starts off with an act so horrible that not a single thing in the rest of the saga compares to it. Such things were only implied until the PT came out, but his force choking was pretty damned evil to start with.

Why did Lucas and Abrams include redemption for Vader and Kylo? Because we all need hope. Hope that we can change our worst aspects. And Luke in the ST falls into that line of thinking as well. What if we learned our lesson and changed and then fell back to our old habits. Yes, even that can be changed. It gives people struggling with demons hope of finding a way out. And who knows, the stories of their misfortunes might steer some clear of falling into the trouble in the first place. These are issues as old as our species. Vader and Kylo are fallen heroes. Those who made them fall do not fare so well, but they have the chance to be redeemed.