In my opinion, a symbiont doesn't control
anything. The host personality is altered by virtue of suddenly having access to a multitude of new memories.
Dax doesn't make Ezri want to rescue Worf, or compel Jadzia to fulfill her blood oath. They do those things because they remember loving Worf and making the blood oath. Joran Dax kills people because Joran Belar did. Dax doesn't control his actions.
Verad seems very different as Verad Dax because he just went from 40 years worth of memories to 300 years worth. Ezri takes weeks to get used to the symbiont for the same reason. All the other hosts had training for what to expect. (And even then, Jadzia took quite a while to settle into her new personality.)