Because comparing against a "competent human" is enough of a control group to be sure that it's finding interesting signal in the data and not just exploiting s

Because comparing against a "competent human" is enough of a control group to be sure that it's finding interesting signal in the data and not just exploiting something trivial like race or political clothing. It doesn't need to be better than humans to be interesting. Coming pretty close would do. But if you told me humans score 90% on the same pictures, I'd believe there's something unrepresentative about the sample pictures, because I don't expect humans to have that accuracy.