To be fair, Jadzia wasn't really all that compelling as a standalone character.
Yeah, I tend to agree, but the same can be said of Bashir for seasons 1-3 at least, as another example. The writers kept throwing stuff at him, though, and, while it's a bit of a mixed bag, at least one extremely cool thing resulted from it (Section 31).
Having said that, of course we will never know what would have happened if Jadzia's relatonship with Worf had not become such a focus for her.
In reality, there was probably never really much of a risk with Kira, because most of her stories don't really flow from her role in the crew, but rather from her ties to the Resistance, the Prophets, the Cardassians, etc. There's really not much overlap with Worf at all.