We performed more thorough analysis. With one BRD with at least 2500 base MP, a MNK can sustain combat for approximately five minutes (the BRD must use consumables and the MNK must use Invigorate). Two BRDs in the same party can increase that fight duration for far longer, or one BRD who is able to remain out-of-combat for the entire fight duration (though this appears to be impossible in dungeons and therefore, presumably, raid encounters as well). In case it wasn't clear, MNKs are being used as the baseline physical DPS class for analysis due to having the lowest possible base GCD and highest TP expenditure over time while performing a standard rotation.
However, as mentioned previously, this kind of forced party structure both emphasizes passive TP management and removes a layer of choice and dynamism when forming party compositions. If a BRD can be used in a party to allow MNKs to change their rotations in such a way as to increase DPS, that is positive incentivization to include a BRD. If a BRD must be used in a party to allow MNKs (or PLDs, WARs, DRGs, etc.) to perform actions at all past a certain duration of time, there is no element of choice. In other words, I want to be able to make the choice to include a BRD to potentially accomplish more over a period of 3, 5, or 10 minutes, whereas without a BRD, I can still actively participate in combat for 3, 5, or 10 minutes.