That's true, but I can't see any other way to do a mass metadata update. Not that one hopefully has to do it very often.
If Calibre's Device -> 'update cached metadata on device' looked like it did something, I probably wouldn't have ended up in this state.
But if you don't care about annotations or reading status, seems like it wouldn't be a big deal, other than just taking some time to send it over.
Presumably once I get all my books squared away this time, as long as I make sure each additional one I stick on the Kindle in the future looks ok, I'll be fine. Fortunately, total, I only have around 200 books in the Calibre library (though I have more that have not been added yet).