Sauri's behind Orva for "least grown individual", but he at least seemingly got out from under his mother's spell who had poisoned him against Bernadetta, because he actively acknowledges her intellect and capability and has realized his error in that regard.
their father being a dipshit who refuses to cede the family title to Bernadetta isn't Sauri's fault. Yes, Sauri could step down from the succession battle, but I'd argue that it serves as motivation for him to keep pushing himself forward, which is good for growth. And there's a timer on it, anyway; if he does take too long in finding a fiancé, then Bernadetta scores the succession rights anyway.
You're not wrong, he's still not great, but he has some advancement and progression in his story. Orva.......really was just a meathead from start to finish, and now has a wife who will literally mother him, it would seem (sternly, hopefully).