For lower efficiency when rolling down the road in top gear with the converter locked ... The fault is neither the planetary gears nor the torque converter. It's the way the transmission holds itself in each gear.
Part of the efficiency loss is that automagic transmissions rely on hydraulic pressure to hold the clutches engaged (every gear has a hydraulically-operated multi-plate clutch associated with it - that's how it selects between the various forward and reverse combinations). To produce that hydraulic pressure, there is a pump. That pump requires power to operate it. This loss is not found in manual gearboxes, because once a synchro is engaged then the teeth transmit the power, and there is no hydraulic pressure required to hold it in gear. Manual gearboxes have no oil pump, no circulating oil system at all.
Another part of the loss is that among all the multiplate clutches which are NOT engaged, the plates are still there spinning next to each other, and there is some minor frictional loss associated with this. This loss is not found in manual gearboxes. If a synchro is out of engagement, the teeth don't touch each other and there's no friction between them ... period.