This is fundamentally different. Arthur Anderson was an auditing firm and did accounting. Their selling point was to be the "source of truth" for their client's books. What's that confidence is lost, then no one would hire them for their work. McKinsey, as a management consultancy, doesn't have to be a "source of truth" and offers perspective, which can be neither right or wrong. Management makes decisions on if they want to take McKinsey's advice or not.