I'd take the bet that MDMA + talk therapy is more effective than MDMA alone, based on the theory of action that recollection is not a read-only operation in the brain, and traumatic memories remain as such in no small part due to the intense negative emotions experienced when recalling them. By forcing/encouraging recollection of traumatic memories, while subduing the negative emotions with MDMA, the connection between those strong negative emotions and the memories are weakened.

Basically, the MDMA subdues the negative emotions, and the talk therapy forces recollection. Without the latter, you just have a pleasant trip, but I highly doubt real progress would be made against the trauma.