Not at all...
2 tanks and one DK tank specced for DPS to offtank when required. And I dont know if you have noticed, but a good AOE tank can do as much DPS as dps classes on trash packs.
For a fight like gluth, it is far easier to tank the adds with an offtank than try and kite them and risk a kiter getting one shotted.
Bearing in mind my guild is 4th on the server, I think I know whether we are gimped or not, and we have done sarth 3d 25 man, and got 10 man to 5% on last drake before half the raid ate a lava wave (that was months ago and we cant be bothered to try it again)