it's extremely hard to find people who actually break the groupthink. it's extremely hard to even identify your own groupthink blind spots, let alone cover them with people with genuinely different perspectives. the crude diversity solution seems highly likely to select for people with superficial differences but core similarities.
The diversity that actually adds something to the understating of a problem, is the diversity of ideas and points of view. Putting different races, genders, sexual orientations, etc, just for the sake of appearing diverse, adds nothing to solve any problem.
How can one say an unavoidably subjective viewpoint is beyond doubt?
And this is not merely philosophical. The notion of improvement can be validly measured in many disciplines, and this is true in many disciplines that are under scrutiny for their lack of particular genitalia.