I compared log data on warcraftlogs by looking at the top logs and also the dps rankings. Shadow is consistently behind the Mages, Locks, Hunters, and DHs as the 2nd highest dps. The gaps 10-20% depending on the dungeon.
Shadow does about the same level of dps as Boomies and their top dps logs are on page 2-3 compared to every other class.
All they need to do is give Shadow some more oomf and it’ll be up there. 5% to Psychic Link and +10% more to dots and Shadow will be on Lock/Mage level.