The obvious part of that is how skilled the applicant is at the task to be performed in that role. This is where the "hire the one best suited for the job" argument comes in, and usually where it stops. At least in the case of a group/organisation that will work together though there is the more hidden value of differing viewpoints. That, in itself, also has value. I think there's a clear argument to be made that the value in hiring, for example, a developer with weaker (though still "good enough") programming skills in many cases could be the better option when that developer is expected to bring additional value in differing viewpoints compared to a developer having stronger programming skills but otherwise fitting the norm in the industry/business. That is, for the weaker programmer, the sum of the contributed values might still be higher than for the stronger programmer.
I think, expressing the problem this way, and being clear about it, makes it easier to reason about. If the aspects taken into consideration were expressed in this way in a job application, I would probably be easier to accept for rejected applicants too, possibly both in the parent comment and in the article.
There is however the question of what, exactly, the motivation is for diverse hiring. I'd argue that in a healthy business, it should be what I outlined above; the team is, overall, expected to perform better with more diverse viewpoints. Although, I'd wager a guess that many times is more about the image of the business than actual performance. While the image is important, and of course will affect profit, it would probably be hard to justify, publicly, such hiring choices on those grounds.