How is pointing out that police oversight boards are not always robust or independent an argument against the position that robust, independent police oversight

How is pointing out that police oversight boards are not always robust or independent an argument against the position that robust, independent police oversight boards are a good thing? The example that you give is important because it shows what we have to fight against to get robust and independent police oversight boards. But the fact that it is possible to fail doesn't mean that we shouldn't try.