Pfft, no no.
A fully geared WAR that's properly utilizing it's rotations and CD's can DPS at just over 300, not counting the buff they give to MT's simply for being there. A similarly geared DRG, that's well practiced at their rotation, will, "maaaaaybe," give you 100 more DPS, if they're not dealing with any mechanics at all, in most cases they'll be delivering considerably less then that.
If a group is fully geared and learning the fight, it's better to go with two tanks, and to put as many of the mechanics as possible onto the second tank, so the DPS can focus on DPS. "If," a group has already learned how to do one tank strat, that's another story, but you're increasing the learning curve significantly enough that most new groups at this point, will likely clear it with two tanks sooner than they would if they were doing the one tank strat.