Indeed, all Captains & Mates should be competent in the use of any and all essential navigational equipment. There may be “some” validity to “People who complain about ECDIS are just projecting their own inadequacies”, but you can’t discount concerns over power loss issues, crashing of ECDIS’s, and issues when inputting chart corrections. In a perfect world, none of these problems occur, but as you know in the real world technical, mechanical problems can and do happen. As more safeguards are put into place, there will be a lot more confidence in the equipment. Unless the ship is beginning a new trade route, most of the routes should already be saved in the ECDIS and it’s just a matter of loading them up, checking all the settings and alarms (which the Captain should have made standing orders for), having all corrections uploaded, and running a voyage simulation safety check to identify any hazards in the route.
Your comment “You get a lot of masters who get paid big money to sit doing nothing in their cabin most of the day” suggests that you haven’t sailed above 2nd Mate. That’s understandable, as there are a lot of 3rd & 2nd Mates that don’t have the slightest clue as to the responsibilities and work that the Chief Mates and Captains do. In the Captain’s case, very much of his “duties” are out of sight of the crew. If you do happen to sail as Chief Mate and eventually as Captain it will be a real eyeopener for you when you discover how many few hours there are in a day compared to what is “your job and duties” require and what expected of you.