In real life, people do dumb things. In mythology, people do dumb things. In fiction, people do dumb things.
Here is my take on Rose saving Finn. Finn was doing a dumb thing and Rose did a dumb thing to stop him. It doesn’t matter if Finn could have succeeded. Rose’s part in that scene is to prevent Finn from dying. It is part of the trilogy. The purpose of Rose in this film was to take Finn from a rebel ally to a full on rebel. She is a rebel and sees Finn as one of he heroes, not realizing, as we do, that he has his own agenda. She sees him leaving and doesn’t see why and thinks he is deserting. He kind of is. But the great thing about Rose is that she is a full fledged character herself. She is technician who just lost her sister. He loyalty to the cause brings Finn around to the cause. His character development was to stop running and stick around. By Crait, he becomes willing to sacrifice himself to save others and become the hero Rose thought he already was. While the Canto Bight sequence and the infiltration of the Star Destroyer ultimately fail, thanks to them hiring DJ instead of who they were sent to hire, the sequence turns Finn from an accidental hero into a true hero. Rose saving him prevents the waste of his life and preserves him as a hero for IX. It also provided an interesting side character.
In the same way, Poe’s part of the story turns him from a heroic rebel into a heroic rebel leader. In TFA and the start of TLJ, Poe is willing to take risks to gain a victory. He doesn’t understand about conserving your resources or making the tough decision to withdraw and fight another day. Leia and Holdo know this lesson well and push Poe to teach him that lesson. He learns it. Instead of trying to fight to the end on Crait, he looks for a way out and a way to fight another day. He went from a reckless hero to a leader hero. He’s probably still reckless, but he has learned a valuable lesson. It is ironic that in light of Carrier Fisher’s death, that his character is ready to take over for her as leader of the rebellion. Even the dialog moves things that direction.
Rey faced her greatest fears. She was waiting for her parents. If what Kylo said is true (and I’m pretty sure it is), then she has to face that they were never coming back. She had turned to Han as a mentor and now turns to Luke, but Luke turns her away. He cannot help her and she must help herself. She goes from waiting and relying on parental/mentor figures to standing on her own. Since Luke will not teach her, she takes the ancient texts so she can teach herself. She sees a vision through the force of Kylo and thinks she knows what it means and finds out it did not mean what she thought it did. He did not turn. By the end, she is alone and okay with that.
And Kylo. He is the Skywalker in this trilogy. Who can say what his fate is but in this film we saw him go from being even more torn inside than ever because he killed is father to firmly on a path when he decides to kill Snoke. He also saw a vision of Rey and thought he knew what it meant. But she did not join him and he is left alone as Supreme Leader. Now what is path is, I can’t say. But as a follower of Darth Vader, it is currently a dark path.