The reson for a human being on a train to 'supervise' is neither commercial nor psychological. The driver is there for the situations that are not forseen. Such include track works, obstacles, weather conditions and the occasional suicide.
And the unforseen events in aviation are far greater in number than on the ground, regardless of what the 'experts' say. I would go so far to say that each and every flight has unforseen events that are simply handled routinely by an aircrew.
And, yes, any crew needs proper training.