That is an excellent concern. I've not generated my initial analysis of the concept of rhetoric yet, but it is a common topic in the wiki (it's a word I have wielded hundreds of times in it so far). I have a lot to say about it, but I don't want to flood you. So, I'll hedged-conservatively ack in our dialectic here. I suggest that whatever is normatively valuable about rhetoric can be analyzed in terms of rightness or beauty. When rhetoric is used wisely, it is a justified beautiful hack in expression.
That's an interesting postulated relationship between three of the four normative sciences. You've covered logic, aesthetic, and ethic. How does rhetoric relate?