I don't think Ezri was the worst character in DS9, but I do think she shouldn't have been a main character because of the time they require and that there was only 26 episodes left. Of course adding Vic also didn't help
If you're not going to kill Dax you have to bring it back, but you could have done that in one or two episodes. In these episodes you could deal with Sisko, Worf and Bashir and then the new Dax moves on. I almost feel sorry for the symbiont as it seems to be stuck in a holding pattern of its former host's life.