If you feel we found out too little about Jadzia and her history, that has nothing to do with one's assessment of the character herself. That's a criticism of the writers. I thought this thread is about why people do or don't find the character likable, not about whether they feel the character was suffiently explored in terms of background and history by the writers. I figured it's more about how she was (behaviour, personality, attitude) not who she was (backstory, nature).
One reason why might not like (it was asked why we don't like Jadzia, not why some perhaps dislike her) a character is that we don't learn a lot about them.
Another is that we don't understand where negative characteristics are coming from, that might lead us to forgive them in other characters.
And in 7 years, we learned more about Ezri in one than we did with Jadzia in 6. I know Jadzia had to carry the wait of also introducing the symbiont, and I think that was the best part of her character, but it would have been nice in the later years to learn more about her. Actually now that I think about it, I think we found out more about Curzon than we did Jadzia, and Curzon wasn't even in the series. That's weak writing I think.
Yeah, Curzon was better explored than Jadzia - I agree, weak writing. And not calculated to instill a love of Jadzia.