Instead of putting DPS in the center, the tanks and healers go in the center with the DPS on the panels. The reason for this is survivability. Those adds can only be TAUNTED to get aggro on. On BLUE and PURPLE phase 2 adds will always spawn. It makes more sense to have two tanks available than one on the panel.
The adds only come once every 45 seconds or so. With a single tank, you can burn your AoE taunt every time and get them both.