It's not just one defensive metric, it seems to be just about every defensive metric, rating or analysis out there. Dame and CJ are both quite good offensively but I don't think that with both of them as bad at defense as they are and being the first line of _efense, that the team can be contenders. I also believe that CJ will have enough value that you can get someone who might not be quite as good on offense but much better on defense that can also help cover for Dame like Matthews did.
You can cover for one but it's tough to cover for both. I like them both.....just like Warrior fans like Curry/Ellis. They were PISSED when Ellis was traded. That worked out fairly well. The history of the NBA is not replete with successful franchises with 2 offensive minded, non-defensive, undersized scoring guards that don't pass a lot between the two of them except mostly to each other.