If most of their subordinates are on a 12-on/12-off schedule, two people who don't do physical work can be on the bridge whenever necessary.

That's why I said "the role" instead of specifically that job title.

Either they're slacking or there aren't enough, and you can fix either problem with 10 quality candidates per ship.

The role here is supposed to be that the big boss watches so that everyone behaves. Plus so that big boss takes blame. It is not like that person would be required for something active.