@davidd I think it's just to me personally, when I do get to have a good glimpse into a character like Susan I can give her credit and some benefit, when the author gives her some good and bad traits which is also very important to me. When he offers a three pages character given to such a good structured character like Caspian I can't really take her personality as valid and well thought, because it clearly works as romance trope. Since we don't know much about her I gave her a unique role in my story even though she remains Caspian's queen but in another level.

The reason I always claimed that Ramandu's Daughter isn't a good queen is because she grew up in an isolated island with limited vision of the outside world and she also lived with the belief that violence is immediately punished by a sleeping spell. Of course that doesn't reduce her character entirely but it also doesn't make her capable of ascending to a throne immediately, just because she is beautiful and for the reader not to know who that queen is to the side of such an important character. Imagine living a peaceful and utopian life and then suddenly you have the responsibility of a kingdom in politics, life changing choices, possibly poverty and struggles. And Caspian chose her because she was beautiful, a quick and irrational decision to be honest.

We actually get a good glimpse of Susan as a queen, her poise, her confidence and she even experienced great adventures, life lessons, a life where she has missed, was hurt and even as you said had struggled in school. She learned how to be a good queen to her people through the years of her reign but before that she learned what the struggles of those people were. We know her and she has known life. In my own opinion a good and true queen is someone who knows her people well, good will and intention is never enough. 

This is why I believe Caspian probably reigned in solo and maybe it took a decade for Lilliandil to adapt as a queen, probably after being struck by the harsh reality outside Ramandu's Island. This is maybe the reason why they had a kid so much later and it's a strong topic I am discovering in my own story as well, where Lilliandil faces many brutal realities of the human nature, how good intentions are not always enough and how heavy the responsibility of a high position can be. 

Lilliandil worked as a trope, Susan worked as a character. And I always value characters more as I have stated many times.