I don't buy that comparison. A Trill enters the joining voluntarily, he's aware of both parts prior to the joining and the composite entity, so in a sense both Trill and host continue to exist. Tuvix didn't. His was a real composite personality.
First of all, that doesn't make sense; why should consent or its absence have any bearing on the outcome of joining? That's a complete non sequitur. Besides, we have
seen at least one coerced Trill joining, when Verad stole the Dax symbiont in "Invasive Procedures." And the merged Verad Dax entity was no different from any other composite being we've seen in Trek.
And he wasn't just a combination of those 2 characters, he became a character of his own, made his own experiences.
Which is exactly how Trill joining works
. If you think that a joined Trill is two distinct personalities sharing a body, then you're astonishingly wrong, and I have to wonder if you even watched DS9. The two minds in a Trill joining become one inseparable whole. There was no more distinction between the Jadzia part and the Dax part of Jadzia Dax than there was between the Tuvok part and the Neelix part of Tuvix. They only became distinct again when they were separated.