I have mained this Priest since Cataclysm, so yeah I am having fun. 
Shadow can be squishy. I have done most of my questing as Shadow, but anything that gave me issues then I switched to Disc. Probably nothing to do with Shadow itself, I am just experienced with Disc, but have only fiddled with Shadow offspec since last expansion (and only for WQ at that). I’ve done Torghast as both Shadow and Disc and haven’t had an issue with either.
That said, if I was going to switch it would be to my Druid. I have been debating changing for the last few expansions, but I love my Priest so much I end up just having Druid as main alt.