You all had me convinced that I had basically read The City and The City wrong, but then I found this review:
Each of these represent a leveling-up in our understanding of the city, another veil tugged aside to reveal the true nature of the city. And the more we learn about it, the clearer it becomes that that truth is entirely mundane, that there is no magic mandating the separation of the cities or the existence of Breach, but simply tradition and human perversity.
What Niall and Dan read as confusion, however, I see as a deliberate, and purposeful, dismantling of the fantasy genre and its core assumptions. …The better, I believe, to thoroughly undermine the genre when it’s revealed that there is no border between the cities except in their inhabitants’ minds, and that Breach is no more magical than any other civil authority
And then this interview with Mieville:
This is impossible to talk about without getting into spoiler territory…
But, yes, the overtly fantastical element just ebbed and ebbed, becoming more suggestive and uncertain. Although it’s written in such a way that there is still ambiguity—and some readers are very insistent on focusing on that ambiguity and insisting on it—at the same time, I think it’s a book, like all of my books, for which, on the question of the fantastic, you might want to take a kind of Occam’s razor approach.
So I can at least take solace that if I am a complete idiot, at least I’m not alone.