My mistake for not being more clear. What I meant in my previous comments was that any of her lines that are of any use,
can have been given to either O'Brien or Kira or Nog or a whole slew of other characters.
The vast majority of those lines you listed are completely generic and inter-changeable with one or more of them.
the lines you have listed by Jadzia that have plot-value or entertainment-value
are inter-changeable with either O'Brien, Kira, Nog, or another character.
Those few lines that are not
inter-changeable, are completely useless. They do not add any value to the show; neither plot-wise nor entertainment-wise.
There are a few lines delivering totally unfunny 'Trill jokes' that 'only Jadzia could tell', but the show wouldn't be missing anything
without them -- rather, it would be improved
. Likewise for Jadzia dictating some boring statements about "Curzon did this, Curzon did that..." in the most mundane, uninteresting way possible.
It's not correct that's she the only person who could serve as a sounding board in ITPM. Tons of characters could have done that. Garak, Kira, O'Brien. It's not like Jadzia did or said anything compelling in that scene that any of those other characters couldn't have done just as well, or better. If they were 'role-playing with prejudice' then the Sisko could have told them to cut it out, and got them to do it properly. Or found someone else if they continued to not comply with that. I don't think they would have displayed prejudice at all though since those characters already had episodes of them dealing with and overcoming their prejudices. It wouldn't matter if Sisko went to Garak about the roleplay, it's not like he was planning to do anything devious at that point when the roleplay occurred. Simply a clean discussion.
The concept of Dax having lived longer than anyone was never utilized well on the show. A great concept on paper, but they did absolutely nothing with it. There's actually a quote from Farrell that is relevant to this:
In fact, the crowd roared after she told one fan of the early DS9 days when, at 28, she faced playing such a weighty equal to the enormous presence of Avery Brooks' Commander Sisko. "'Just go watch "Star Wars" — you're just like Yoda'," she recalled being told, and then made a face: "Well, THAT was no help. "
It's correct - that was no help. Jadzia did not come across like Yoda or like someone who is wise. Her supposed extremely long-life was not at all congruent with her acting, or the writing behind her character.