Is TDMA optimal in the low power regime?

We consider two-user additive Gaussian noise multiple-access and broadcast channels. Although the set of rate pairs achievable by time-division multiple-access (TDMA) is not equal to the capacity region (achieved by superposition), as the power decreases, the TDMA achievable region converges to the capacity region. Furthermore, TDMA achieves the same minimum energy per bit as superposition. Despite those features of TDMA, this paper answers the question in the title negatively except in two special cases: multiaccess channels where the users´ energy per bit are constrained to be identical and broadcast channels where the receivers have identical signal-to-noise ratios.