Fascinating thread. I almost completely disagree with the OP.
The thing with Ezri is two-fold. One, when Terry Farrell opted not to return, they had a choice how to handle her departure. Two, they had a choice when it came to replacing the character, ultimately leaving the show sans science officer.
To my thinking, they could either
- Not Kill Jadzia: Promote her away, difficult since she's married to Worf and you would expect them to maintain regular contact, but might've been interesting for Worf
- Kill Jadzia, and write Dax out: have Dax's next host show up long enough to have some emotional closure
- Kill Jadzia, and bring in a new Dax (as we saw)
In scenario 1 or 2, you have the option of not bringing in another full-time character, but with 3 you pretty much had to. I think the creative team simply chose to take the bull by the horns, and we ended up with a pretty good character, who, I'll admit, was a bit of a distraction at first. However, they made her rather integral with Sisko and Worf's recovery, so that was good.
Personally, I think I'd have preferred the first option. It still also kind of bugs me they never seemed to have a science officer again, but then again they never seemed to need one, either.