Yeah, Berman's apparently no better in that regard than Roddenberry was. I don't blame Farrell at all for wanting to get out of the show. If he hadn't been so stupid maybe she would've been included in the finale. She was, after all, one of the actors listed in the start credits for six seasons. As you can see, this is something that bugs me and I can't let it go.
ETA: I think that the last season featured Ezri more than it would have featured Jadzia if Farrell had stayed, and I don't think introducing a new character in the last season worked at all (nothing against Nicole de Boer, she did a decent job with what she was given). Either Dax should have died along with Jadzia, or they should've given the symbiont to a random Trill visiting DS9 when Jadzia died who would then leave the station never to return. I never liked Worf and Jadzia's relationship much, but Worf and Ezra's brief attempt to continue it was cringeworthy. Or else Ezri should've gone back to Trill to better understand her new joined life instead of staying on at Sisko's insistence in Afterimage.