In support of which: the examples I gave from the Mediterranean and Eastern Europe are music where the whole piece is conceived as polyphonic from the get-go. In some cases they don't even have the idea of a solo song, so they didn't arrive at those results by starting with a tune and "arranging" it.

Even in the Sacred Harp stuff, it can be difficult for a listener to pick out one line and say "that's the tune", although it may have started out as tune arrangements. (And traditionally there were no non-singing listeners anyway).