Justification that 'good exposition' is uniquely defined
This is a false dilemma. Good exposition is not uniquely defined.
Yet, if a referee claims they don't understand what you write, chances are that they are right. Add some clarifications. This doesn't mean necessarily rewriting everything with the referee's favorite approach: maybe just a remark tailored to people with their background. ("If you're used to seeing concept X defined in this other way, note that this is equivalent because...") If there is a wrong approach that you wish to refute, do it, in the paper or in the response letter.

Good exposition doesn't mean the referee's preferred viewpoint, but it doesn't mean your preferred viewpoint either.