The more i sit on it the more I realize the game is more about Atreus' journey than it is Kratos, and in this way is why you get the impression that Kratos is used to tell other people's stories, at least in the grand scheme of the game.
In terms of character progression I think it works. Kratos has changed, he's older and more importantly he is tired, he just wants to fuck off and live without anyone bothering him, he doesn't want to take up the fight to anyone but will absolutely do so if necessary. However he has a stupid kid who's hellbent on stirring the pot and he has to protect him.
Kratos is a flawed character who's emotions and actions are dictated by his past experiences, he's protective and wants to be different because his approach last time did not work and he ended up murdering his family. Here he has lost his wife again so he clings to his son in an effort to not let history repeat itself once more. By the end of the game he is redeemed by his choices, whereas his choices in the past condemned him to a life of suffering and nightmares.
If you go back to the first game, he did what he did to be rid of his memories and nightmares, he doesn't want to keep suffering, but he is denied by the gods. In 2018 after what I assume is many lifetimes, he's been able to move on, his whole demeanor towards gods, war and killing is grounded in this.
He says he doesn't believe in prophecy but he's got a death prophecy hanging over his head and that terrifies him, he doesn't want to live his kid alone in a world that is trying to manipulate and kill him.
It is exemplified best in the story he tells Atreus before Ragnarok about the old man who can no longer carry the logs on his back and wishes for death, then when death comes to his hear his call he instead asks her for help to carry the logs, he wishes to keep living despite being old and tired.
When he discovers the hidden mural at the end of the game he sees people worshipping him as a god on an altar, a path he never believed possible he tells freya. And it goes back to his encounter with Odin as well, where he tells him he doesn't know anything about godhood, about having people loving him because all he is good for is destruction.
I am personally happy this is where they took his journey, having him die in a blaze of anger would have done nothing we havent seen before.