Diversity doesn't matter in practice if management doesn't want to spend the resources to engineer for diverse use cases. I've been over-ruled too many times when I've pushed for "fringe" use cases - including once with exactly your example of a product not working on Black people (different product, but same ethnicity-based issue). My team intentionally sought out (internal) diversity to test the prototype on. And guess what? When I said this was a big problem and we needed to fix it, I got over-ruled (by my non-White company president) because we were already late shipping the product. (Then product got canned for other reasons later - after I left the company shortly after this decision).

I'm not sure how to fix this broader problem - or what else I could/should have done there (other than leave for greener pastures)!