For point 3. I believe Airbus has a lot of commonality between its cockpits on different aircraft, so it is easier to get type certified on an A350 or A320 if the pilot already has a rating on the A380. This means the reserve crew can fly the other smaller planes when not required for the A380. Boeing has not had this commonality until recently - I think it was a selling point for the 787 that it had the same cockpit layout as the 777, thus minimising crew training.