So what's the claim here? If an employer wants to hire only white men (and no hardscrabble backgrounds, please) regardless of qualifications that should just be allowed? That we should have a permanent underclass instead?
I don't necessarily agree, but note this Malcolm Gladwell argues in Outliers that this is exactly what happened to Jewish lawyers in NY in the mid 20th century. White shoe firms wouldn't hire the Jewish lawyers, so they started their own firms and focused on "distained" but ultimately highly lucrative areas of law.
Also I'm pretty suspicious of Gladwell. He spins a good yarn but his work is less than rigorous.
Historically, the marked exploiting cheap resources was so pervasive that we generally needed the government to prevent it. For example, to prevent employers from hiring cheaper negroes over whites, we passed Jim Crow and Davis Bacon laws.
https://en.wikipedia.org/wiki/Davis%E2%80%93Bacon_Act https://en.wikipedia.org/wiki/Jim_Crow_laws
Of course we assume, in this thought experiment, that all the other things Company Bigot could do to become more competitive (invest in more employee training, better infrastructure, etc) are also available to Company Diversity. This isn't always the case. Maybe Company Diversity's hiring practices have alienated it from potential suppliers or clients who prefer Company Bigot's views.
Specifically I'm thinking of Japan, where (apparently; source: this site) the cultural emphasis on the salaryman paradigm means that hiring from the significant pool of contract labor can hurt your company image as far as working with the established corporations is concerned.
Wouldn't surprise me. Considering we're talking about legal firms, a good chunk of the job is social interactions: with the clients and their partners, the judges, etc. If we make the not-exactly-absurd assumption that white men are more likely to be perceived as sound, then they could in fact "perform better" than others of the same ability.
Which is why it's often considered even more problematic than individual discrimination, but also often easily dismissed, since the actors don't consider themselves as biased, they're just doing what's "reasonable".
"Instead"? We have one now.