I thought this was a serious question, but now looking back on it, I see it might have been just a joke I fell into. Oh well, I tried to be helpful. I won't do it again. I promise.
David, this was absolutely a serious question. I joke with Bud all the time so don't let that distract you.
One of the reasons I am not very fond of much of the music being produced today is that it has little or no melody. It is basically rhythmic sound. You can not hum rhythm in the shower. Melody is what we remember about a song.
I can play you famous chord progressions and you likely can not name the song. I can also play you rhythm patterns from well known song and you can not name them.
I assume if a person went to a serious music school and was well versed in music theory they could describe some complex ideas about melody.
I don't have that sort of education so I ask questions here and many other places.
Your post was intelligent and was exactly the sort of discussion I was looking for.
There are skilled vocalist who have beautiful voices that sound second rate do to poor melody or "top lines" that they are singing.
I am not trying to reduce melody into some un-alterable algorithm but there must be a way to make better guesses at what would sound the best.
I am sorry if my post are verbose but I don't know how to express most things in one liners.
Billy