I dont agree to this two points.
The commando joined the NSG to save his country, not to polish the boots of his officer, however superior they might be.
The NSG are issued rifles an not polish brushes.
Insubordination is only when a commando disobeys his commanding officer which pertains to his duties and polishing the boots is not his duty by any stretch of imagination.
Secondly, if he had written a letter to the DG in private about his superior do you know where it will end up ?? Straight in the dust bin, unopened and unread. He had to go public so that the media tracks it. Sad reality of the Indian system !