Put it this way: Guinan almost could have appeared in TOS. She is a kind of character everybody recognizes, and a lot of people like to talk to: a bartender. Bartenders are universal. They'll always be needed. They say things that make sense
Troi? That's pedantic psychobabble all right, but it was Gene Roddenberry's. By the time TNG came around Gene was fully immersed in it. That's why the first season was so wishy-washy. Gene bought into all that. If not for that psychobabble, the writers would never have thought that a show set aboard a starship would need a 'counselor' in the first place.
Although: In the Voyager
relaunch, there is a counselor as well, but it's a guy named Hugh Cambridge, who is apparently written to resemble Gregory House. Can you imagine HOUSE as your counselor?