If you have a fixed headcount, then forgoing one candidate for equivalent another doesn’t carry a cost. By hiring person A you would be missing out on person B,

If you have a fixed headcount, then forgoing one candidate for equivalent another doesn’t carry a cost. By hiring person A you would be missing out on person B, by hiring person B you would be missing out on A. The point is that the net cost is 0. So if B brings more diversity then A you should hire B. You are not (net) missing anything.