Gene Roddenberry was an ideas guy, not a writing guy. It was very forward-thinking of him to suggest that mental health would be important enough in the future for a ship's counselor to have equal importance to the ship's first officer, with their own seat on the bridge next to the captain.
But then he never fleshed the idea out any further, the "ship's counselor" was never given any real job, and by the time the other writers realized the problem, presumably everything about how the Enterprise-D crew would operate was already set in stone, so now we have Deanna Troi, ship's counselor, who's going to be in pretty much every single episode, always there, who has basically nothing to do unless the episode is explicitly about Her. Hell, her mother, the occasional side character, is far more interesting than she's ever allowed to be.
Like yeah, Picard wasn't able to leave the bridge or the ship that often because of his importance bla bla bla, but Troi probably spent 90% of her screentime sitting quietly in a chair, with the occasional cut to her with a Concerned Face to remind you she exists. She's as much set dressing as Michael Okuda's LCARS panels.
