You all are forgetting that she's a symbiont. She's part 300 year old slug AND 25 year old science officer.
What Teacake is saying is right though...what's the point of even making her Sisko's old buddy if that's only relevent in a handful of eps.
The problem is, it's cool and all that she still is an honorary Klingon and gets involved with Kor and Kang and Koloth...but Jadzia is so NOT a badass, that it just doesn't work.
But like I said at the beginning, she's a neutral for me.