You are right in thinking about the frequencies of a song. Lower voiced songs sound great with an acoustic guitar's fingerpicking of the higher strings/notes, as well as the upper keys of a screaming B3 during a chorus etc.

It is all about the overall sonic quality of a song that makes it easier on the ears. The lows during a verse, building the tension for the listener and then when the highs kick in during the chorus etc.

You are on the right path in asking these types of questions.

Good luck.

Trax