Not a loss. As a member of the President’s Cabinet, Dr. Carson’s voice would necessarily be subordinate to the President, while as an outside consultant, he may be overruled, but not subject to a diminution of his influence.
I see Dr. Carson as an advocate of a number of positions on which the Trump Administration has to either soft-pedal, or have at least the appearance on not supporting. A sounding board is not necessarily an echo chamber.
Is this official? I’ll wait for another source.