Without basic DR and map reading skills, you are building on sand. Successful DR requires an in depth understanding of basic navigational and map reading principles. There is no quicker and cheaper way to demonstrate mastery of those vital basic competencies than performing DR.
Furthermore, without those basic DR skills, what chance has our little button pusher got of detecting a GPS failure or wrong button push?
If you want to know real terror, wait till you loose all those avionics you relied on when a battery or alternator fails and you have not got access to a map, pencil, watch and magnetic compass.