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.
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.