My two cents:

I think what everyone's looking for with diversity is the diversity in opinions, in walks of life. There are many ways to consider that kind of diversity, from education and income to culture and age.

At the same time, the various systemic problems that arise with homogeneity and discrimination are difficult to address without resorting to abstract categories (like race, gender, etc.). Like you say, the judgement of diversity is over measurable things like melatonin because it's quite difficult to assess "nonstandard backgrounds" otherwise.

As an example, I had a first company-wide meeting yesterday at my new job. I was happy to see quite some diversity in age, gender, race and political affiliation - my previous gig in the same line of work was like 80% white dudes. However, nearly everyone has a college degree, so it's not very diverse in that regard. However however, that is to be expected with this kind of work, so it's probably not such a problem.

I dunno. Diversity is important and should be pursued, but there are limits to what you can achieve in certain fields and that needs to be taken into account. But those limits also shouldn't be used to hide ideas of superiority.