Not untrue, but in your counterexample you've compared the workload (and review quality) that can be handled by 2 people (D and O) with a single person (D&O).
A review from another D&O could be required as easily for production code as an O's review for D's code.
If you're trying to replace a D and an O with a single D&O, you're doing something wrong anyway.
But on the other hand, in your model performance and stability are solely part of O's business. But D has to be aware of those issues if you want him to code with them in mind. and they WILL be on the mind of a D&O