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To compare it with ENGINE SUMMER, a comparison mantis made (though apparently he didn't mean by it what I took him to): in ES also, the protagonist's story is not resolved in the sense we had expected it to be; instead, a sudden twist of events abruptly "closes off" the protagonist's story. But in ES the resolution worked, and I didn't feel cheated, because it was emotionally moving and thematically resonant. Neither of these things are true of the ending voyage in RttW.
While I did not "dislike" the ending as much as some here did, I think you have a good point. Suddenly "Horn" is "Silk." Suddenly they all go away. This has not been "prepared." And as you note, unlike Engine Summer, the ending is not emotionally powerful.
But Wolfe often does this kind of thing. It's his way of trying to get us to re-read the book or story with new eyes. Yet, the re-reading does not seem to give much in this case.
Nutria
*This is WHORL, for discussion of Gene Wolfe's Book of the Long Sun.