Realistically it doesn't matter. If you're moving the add, or Bahamut, you're still losing DPS somewhere. If your DPS is strong enough you don't need to have all 4 DPS switch targets. We usually leave 1 melee DPS on Bahamut full time. Plus, if your DPS go crazy before the OT hits it, there's a strong chance it's going to beeline for the healer, so there's at extra GCD DPS could be on Bahamut anyway, whereas moving Bahamut you might lose that. Furthermore, it's pretty easy for the OT to move the add into position seamlessly once they have a feel for it. Should result in less DPS loss than moving Bahamut. Also, side note: no real reason the OT should be using Tomahawk/Shield Lob on the add. Only if they want the extra damage while pulling it away. They're terrible options for actual DPS.