Kylo can't be the main villain because they didn't develop him and they wrote Rey to be super Jedi Knight with no training.
I think they developed Kylo enough, though it is mostly Driver's acting that is doing the heavy lifting. Him being beaten by Rey in the first movie I never had a problem with. In the following movies they kept incrementing her powers futher however, which is where they crossed a line.
You don't see Vader losing or whining in the 2st two movies.
Kylo Ren doesn't need to be a Vader clone. In fact, he shouldn't be. His conflicted nature and weakness is what makes him interesting as a character to me. His loss against Rey is the first step to changing him from an antagonist to a possible ally.
So you had to bring back Palpatine or have Kylo as a weak villain.
Kylo Ren's conflict was already set up in the first movie. I don't think he was meant to remain the main villain throughout the whole trilogy. But they shouldn't have killed off Snoke quite so early.
If they had put things in a different order, is Rey smacking down Kylo in part 3 not part 1, Snoke dying part 3.
They could have gone that way. But I thought that the idea that Rey was stronger with the force than Kylo was an interesting angle. I feel they could have explored the idea of her being some sort of anomaly within the force. A flux or divergence, instead of a direct child of a character we already know. I also like the idea that Rey is drawn to the dark side, where Kylo is drawn to the light side. There's an interesting dynamic there, which they kind of explored in The Last Jedi. If only they would have had a better pay off. But I guess that requires good writers.
Rey didn't need to be related to anyone but she needed a relationship but they didn't do much there. Reylo doesn't really work when you think about it.
Indeed she didn't need to be related to anyone. But when I think about it, their relationship is the most interesting angle to explore for their characters. They are both force sensitive and both being drawn to the other's side. It makes sense to explore a relationship that is somewhere in the gray. But I think The Last Jedi really missed a great opportunity to have both abandon their respective sides, instead of Kylo immediately returning to evil after their big team up battle.
Rey could have been Luke's star pupil where she met Ben. She would have had a preestablished relationship with Kylo, already a Jedi Knight, Luke doesn't come across as a failure etc.
I'm not sure how I feel about Luke being a failure. On one hand I feel that all characters need new trials and tribulations. You can't have Luke being happy and successful, and you need a reason why he is living on a secluded island. But on the other, I feel The Last Jedi inserted things that didn't seem to fit his character.