My impression is that this pair of lexemes has reversed in that respect of the last 20 years or so. In the late 80s, "diversity" only referred to groups, and "underrepresented" was often used to refer to an individual, especially with respect to discussions of affirmative action and the like. Unfortunately I spent the late 80s in Berkeley, so the Berkeleyness of discussions I would have been hearing at the time may disqualify that data point.