I think for the reader, it's important to see the mistakes that all of them make. The princess's fault was her arrogance, and I do think she should've suffered consequences for it, but perhaps not the consequences that she did. Her father's fault was making a foolish vow because he was angry with her, and not thinking about what might've been best for his child. And the young king's fault, I think, was achieving the right end through the wrong means.

But that's just what I've come up with, from thinking about it. I don't think it's a very satisfying fairy tale, really.