Yes, I think you're right. (Also, heh, that poem has occurred to me as one that'd make a perfect epigraph for this book/Broster's work in general).

I think if you really wanted to make something like that work, in fix-it fic or otherwise, you'd have to get really into the details of why Keith sees capturing Ewen as his duty and whether that's inevitable and all the messy political details of his allegiance and his status as a soldier, etc. etc., which could be terribly interesting but is not at all what's happening here.

—except, there are those hints which tgarnsl pointed out last week, that Keith's identity and particularly the part of Keith that has learnt to care about Ewen can be disassociated from military duty, and perhaps that would be a truer and better thing, and perhaps that could be done convincingly and satisfyingly... and so the idea keeps picking at me, as I said. It's good fun...! :D