Comparing ethnicity to a disease is, at best, an odd choice. Equating them would be a false equivalency.
If you don’t think demographic representation is inherently valuable I doubt there’s much I could say to convince you. Although I would strongly suggest you consider how disproportionately (and not accidentally) Native Americans and other minority communities suffer from pollution and environmental hazards as just one major policy example but an excellent starting point for your research.
If demographic representation isn’t consequential then legislative politics would remain completely unchanged if we replaced every last wealthy old white able-bodied straight man in congress with a not-wealthy young disabled gay minority woman. I’m just not seeing that.