Part of the fun of watching a TV show or reading a book is in the character moments, especially since character-based dialogue is one of the hallmarks of DS9. Maybe her initial direction was that she was supposed to be Yoda-like, but characters evolve from where they are on the page in large part because of the writers and the actor collaborating (the degree of collaboration differs of course).
The "Trill jokes" aren't just jokes about being this particular kind of alien, but from her point of view of what it's like to be that particular type of alien. She was a character at peace with herself. The lines spoken by her could not have been spoken by Ezri becuase she was someone who was thrown into being the next Dax host out of unusual circumstance.
The reasons I gave for Dax being the sounding board in ITPM were character-based reasons. Could the other characters you mentioned have done it? Yeah, but why have them do it when to the writer it was a more interesting choice to have someone like Dax do it. She knows Sisko well enough that doing the seen as a role-playing exercise seemed more natural. If it was one of the other characters it would have been akin to the expository Observation Lounge scenes in TNG, it might have been okay, but it would have been expository filler to connect plot points. Storytelling isn't about getting to a destination but the fun you have in the car on the way.