But Rather?

My former student Paolo has a question.
It's regarding this sentence:

"The Yin and Yang does not simply focus on mutuality, but rather compromise."

I'm not sure if "but rather" is a grammatical error. Should I use just one of the two? Which is better, "but" or "rather?"

I want to do a whole lot more to this sentence. Maybe something like this:

The Yin and Yang do not focus simply on mutuality, but also on compromise.

Yin and Yang make a compound subject requiring a plural verb. "Simply" needs to be closer to what it modifies—not "focus" but "mutuality." I'd use "rather" only if I had completely denied the first trait:

The Yin and Yang do not focus on mutuality [at all], rather on compromise.