I think that's a question for the experts.
It's true that people often use that exemption. On our end, the analysis criteria are clear to my analysts and me, because we run the test all the time. However, we find that in other institutions, there's often turnover among analysts, so they don't have all the experience required. As you said earlier, it's easy: as soon as people see a document classified as confidential, secret or top secret, they tend to think that the information should be hidden or shouldn't be disclosed. In reality, the test goes further than that. For example, we need to determine whether there will be consequences should the information be disclosed.
Over time, the need to maintain the confidentiality of records wanes. That's why we need a declassification program. That way, experts could go through the records and automatically restore access to those that are overclassified after several years, as is often the case.