I don't listen to a ton of metal. Mostly Jazz, progressive rock, and electronic downtempo...so I guess of a lot of that is purely instrumental, but I do get where you're coming from...

I don't necessarily agree with your second point though. Music is subjective to the listener, and anyone can engage in music in any shape, way, or form they want. Depending on the genre, theres a good chance that the melody and rhythm came before the lyrics, otherwise the lyrics wouldn't fit the context, or timing of the song, and you could end of with "scrambled eggs". Think of any big rock band, the melody or riff usually comes first. Kurt Cobain wrote music first, as did Guns and Roses, The Eagles, John Mayer, Elton John. etc...BUT I'd image singer/songer-writers such as Bob Dylon, Taylor Swift, and Jack Johnson write lyrics first, melody second. However, it's more than likely that these things happen organically at the same time.