Well something is wrong here. Either your Omen is lying to you, or something else is going on. There is no way a rogue in T4 gear is generating 2.5k TPS. Rogues have some pretty good innate threat reduction, which would mean that he was doing well over 3K DPS, which is simply not possible at that gear level. If you're putting vigilance on him, then that's even more of a mystery.
I suppose it's possible if he starts DPS immediately and gets a few lucky crits in, but once you get started, everything that I've experienced and read so far has shown that tanks are easily "out-threatting" any DPS who is similarly geared. If your rogue is still somehow managing to pull off of you then you're doing something terribly wrong.