Going off of Turn 10-T11- They have roughly 30-40 less DPS Potential
Turn 12 - 15 ~ less dps potential, depending on the strategy. I for one don't think bennu's shouldn't be mass aoe'd. Mage lB is enough > Single target the rest. But for the groups that have SMN's Baning dots then that raises their potential quite a bit
Turn 13 - ~20 less dps potential than blm, about equal potential as other classes depending on how the add phase is handled. BLM will still out DPS them throughout the whole fight + the add phase.
On a test dummy - 30-40 less dps potential than any other class, sans BRD.
This is of course not considering MP Problems.
At i115 with i110 gear one fester is roughly 8.3 DPS less so their potential goes down even further every time the are forced to use ED.
As most people have said fixing their MP problem would go a long way, Itemization would go a long way as well. A few minor dps tweaks would also level them out. I don't think anyone is asking for an overhaul or an over buff.