Nathan Dowdell - With respect, in our game we had the Ops officer as a "minor character" because we did not have enough players.
I do not see how the game cannot be played without using NPC's in some of these "Roles".
I acknowledge that TNG did not have a dedicated Science Officer, but let's face it - that makes no sense on a dedicated exploration ship.
Why not have this position as an NPC when it is not germane to the story line, allowing a PC to play a character that is important to the arc? I did read your last paragraph, but I guess I am a bear of little brain, and do not understand you point of view in this.
ST:A does not even have a Ships Counselor - yet, since your example is TNG - they most certainly did - so why don't the rules include this "Role"?