'Dax' could have been the defining episode for Jadzia. Sadly, it was mediocre.
As much as I personally liked Dax (I like episodes that depend on verbal sparring instead of the physical kind), I have to agree that it could have been a good episode for Jadzia. That's definitely the biggest mistake the writers made with her character - they focus so much more on the Dax part of her than the Jadzia. The most we learn about Jadzia as an individual is a throw-away line about her sister. Everything else is about Dax - Lela, Tobin, Emony, Audrid, Torias, Joran, and Curzon, especially the later get more development than poor Jadzia. They may correct the mistake with Ezri, but it's still a sad commentary for Jadzia.