Of course, it would be hard to accentuate
her importance in the ship's hierarchy without showing her rank...
But that's what they did for five seasons. Hell, when "Disaster" originally aired, I had forgotten
Troi had a rank at all. I had completely forgotten she had been depicted as a Starfleet officer in the pilot, and had taken to thinking of her as a civilian psychiatrist/psychologist serving Starfleet, the way Guinan is a civilian serving drinks as a bartender.