The personalities of joined Trill are basically meant to be a fusion of all the personalities of the hosts and the symbiote. Though the current host and the last couple hosts seem to contribute the most to this fusion.I also don't think the Dax symbiote ever contributed anything that can be recognised, if that glorified slug had any personality I sure never noticed it.
And stuff like that doesn't really work all that well in fiction if the characters who were combined in this fusion haven't been established beforehand. So Jadzia, especially in the first season was basically meant to be combination of pre-joining Jadzia and of Curzon (at least most of the time). And since neither we, nor the writers, nor Terri Farrel had a very good idea on who Jadzia and Curzon were before their mental fusion (or, really any idea at all), of course that didn't work out very well.
That's also why Ezri worked better, since Jadzia and Curzon had been established by that point and so we saw their influence on her and how she, as Ezri, coped with it.
Like I seriously think Jadzia would have probably worked better if they had Curzon on the show for, like, half of the first season or something, then he could have died, Jadzia could have shown up, received the symbiote and we could have seen the contrast.