This problem of human irrelevancy seems somewhat orthogonal to the alignment problem; even a maximally aligned AI will strip humans of their agency, as it knows best. Making the AI value human agency will not be enough; humans suck enough that the other objectives will override the agency penalty most of the time, especially in important matters.
I am skeptical of your premise. I know of zero humans who terminally value “diamonds” as defined by their chemical constitution.
Indeed, diamonds are widely considered to be a fake scarce good, elevated to their current position by deceptive marketing and monopolistic practices. So this seems more like a case study of how humans’ desires to own scarce symbols of wealth have been manipulated to lead to an outcome that is misaligned with the original objective.