"A whale is no more a fish than a horse is."
This sentence is quite popular among Japanese students(aged 16 to 18) who learn the "no more...than..." structure in English. They call it "くじら構文," which means "whale structure." in Japanese. (There's no such grammatical term for it in Japanese, by the way. It has been passed down from generation to generation, I suppose.)
No, "horse" is still the subject of the second clause. Switching the order round like that is usually somewhat archaic in English, but would work okay here.But... If you move the "is", doesn't it say "A whale is no more a fish than (a whale) is a horse." instead of "A whale is no more a fish than a horse is (a fish)."?
This is not archaic at all."A whale is no more a fish than is a horse"