I did twisting corridors in an offspec and honestly it made very little difference past the first so many floors. Almost all of your performance comes from the anima powers once you get them rolling, so it doesn't really matter what the base spec is when you have to play the powers regardless and they're the same across the entire class.
For the regular stuff, healers are fine in torghast you shouldn't have to swap. If you struggle to solo it you can always jump into groups and do it there in your main spec.