I was so happy when I found country music because I ran into the same issues trying to play and sing rock in my early years. Country singers were singing in a natural voice.

What hasn't been mentioned yet is that most of the groups in BOTH categories also had their own internal songwriters. A songwriter/singer will naturally write the song in a key he or she can sing comfortably and that provides the energy level the writer is trying to get across to the audience.

You are correct about the energy. Transpose a song from one key to another and more changes then just the key. Unless you are careful and attentive to the entire thing, energy levels can and do change as well, and singing it in a different key changes the entire feel, as you have noted.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.