Melee dps when class balancing was going on went like this:
Zerk > rogue > monk.
From what i can tell of the parses and the chat logs. In reality though, all the rogue parses were done with the donor (or so it seems). A NON donor'd rogue can't hope to compete with an equally geared melee dps in terms of dps. I've confirmed damage with my rogue, who has an aged nightfall (the best t6 dagger) in mainhand, to be significantly behind most other equivalently geared melees. To the point where my bots would out dps me sometimes. On FULL BURN, however, they keep up fairly well with quested ring + animal power going. But that's only once an hour. So essentially a rogue has to constantly have a +DMG disc going to keep up any other time; Which means you'll run out of energy, or discs, soon enough. Ranger / Ber can /autowin much easier, and Monk is somewhere between the two depending on their setup.
With the disparity in t8 discs, this gap will only widen. BUT the silver lining (at least for myself) is that the t8 dagger almost catches up on raw backstab damage. /Dream
Your Mileage May Vary depending on group and/or gear situation.