What is a benchmark for diversity of employees by an employer?
How about - the employees in your organization are within a standard deviation of representation percentages in the population as a whole, based on general race numbers ?
A "benchmark" is something to measure against, though, so to say an employer isn't doing this isn't to make a conclusion about the employer. I worked for employers who had large numbers of gay employees, Jewish employees, and Chinese employees that were discriminatory and evil in their own way.
I feel that these discussions need to separate those who are arguing in good faith, who are open to ideas vs. those who are only pushing an ideology.