I'm not sure that's true. What you describe is the case for any individual candidate, but doesn't account for how those candidates interact with one another. Specifically, it has repeatedly been shown that more diverse teams will consistently outperform more homogeneous ones.

If your company only hires above the 95th percentile but their method for finding that quality cutoff is heavily skewed towards a certain demographic, in the long run that company may well perform worse than a company that hires at the 80th percentile but without the demographic skew.