A like a little relief too. I rarely use my thumb, but using my fingers I go from a light touch to hitting the strings like it was a slap with a thumb (like John Entwistle, but not as good of course). I think if you have a straight neck you either have to play with a light touch or you have to be extremely articulate to get a variety of sounds. Or maybe you could say the relief is a way of covering up sloppy playing. (Maybe I should only speak for myself on that!)
Actually I sold my first Alembic over 10 years ago because the neck was too straight. I wasn't able to get used to it, and I didn't know that I could change it.
Mike