She is a poorly written character whose powers are frequently ignored or forgotten by scripts. It’s established that she can sense emotions, intent, honesty, deception, danger, and so on. Yet, even after establishing this, a conman can lie to her face and she won’t notice. She can be surrounded by people who are preparing pull weapons and take the crew hostage, and she doesn’t sense a thing.

Yeah, for some reason she can sense emotions through the viewscreen despite the person on the other end being lightyears away. But even then, her role is mostly to state the obvious, letting us know that the scowling guy who was been yelling at them is upset.

On a more fundamental level, her entire concept is at odds with the rules governing the show. It’s the enlightened future where people are more evolved and we aren’t allowed to have interpersonal conflict or psychological issues. To the point that they were forced to rewrite a script about a kid trying to cope with the death of his mother, because Gene insisted that in the future, people don’t grieve. And of course none of this was enforced consistently, but it did mean that they couldn’t focus too closely on the crew dealing with the kinds of issues that would actually require some kind of psychological help.

At the same time, they also gave a lot of the advice giving duties to Guinan, some of which goes way beyond the stuff a bartender should handle. They even gave Guinan mental powers to further the needed advice in one episode, which makes Troi that much more superfluous.

Part of the problem here has as a lot to do with pacing and expectations. Guinan, being a guest character, gets to pop into existence when someone needs to have their perspective altered with an anecdote or keen observation, possibly while they look miserable at a bar. And then, having prepared our heroes for the climax of the story, she exits the script with another tally in the win column.

Troi, whose official job is providing guidance and therapy, is going to be the first person you talk to when her skills are needed. So sessions with Troi tend to be early enough in the script that we can’t have them solving the problem. Therefore, her advice can’t actually work, so she either misreads the situation (looks bad for an empath), or she just gives very bad advice. For fuck sake, her response to being told “I think the only emotion I feel is anger, and killing gives me pleasure” was to suggest that the patient go explore these emotions on his own, without guidance or supervision.

What we’re left with is a character who mostly states the obvious, who forgets she’s psychic when it would actually matter, who is terrible at her job, and for bonus points, who spends most of the series in her pajamas when everyone else wears the damn uniform.