I was finding similar numbers as Lethality on the training dummy as well. Doing an actual instance dropped down much lower though, because of the need to stop and move, getting frozen/knocked back, all that fun stuff. I'll give Concealment a try again for the first time in a while soon (I've already respecced 3 times since yesterday for various reasons, I don't know want the cost to get too high). I actually enjoy Concealment more but the positional issues and melee unfriendly encounters pushed me out of it.
The sad thing though, is that my fresh 50 MM Sniper with oranges, blues and greens pulled almost the same numbers as my Operative with mostly Rakata on the dummy.
I did notice that snipers were getting slightly higher DPS as I mentioned in my post, and I in fact also tried out the dummy with my fresh level 50 marauder, and he was only pulling slightly lower DPS than out guilds Rakata geared marauder. I don't have enough data yet to make a sound conclusion, but it seems like its about the same for all classes / advanced classes.
One thing I have been noticing about concealment, is that in operations your overall DPS does not drop all that much, since it is more of a "bursty" spec. Whereas if I have to move around a lot when using lethality it is difficult to get my poisons to tick for the entire duration, that or I have to switch targets a lot which is not optimal.
I firmly believe that even with the not so melee friendly boss fights that concealment is still the way to go for the best OPS dps. It just forces you to be more situationally aware.