[ericd]

Good point, but something to keep in mind is that the efficiency of the motors in turning stored energy into motion is only one part of the efficiency of the aircraft. If a plane is able to fly much higher due to the engines no longer being air breathing, that would also change the equation, as drag would be much lower with the thinner atmosphere.

[Gravityloss]

Also you can tune the location and amount of propulsors, and have a high efficiency rotation rate with direct drive electric motors.

The current turbofan engines are close to the size limits in relative fan size and bypass ratio without a gearbox, which adds cost and mass. (Only one manufacturer is in the process of introducing a geared turbofan.)

Because of no high speed jet exhaust and large area thrusters, these aircraft have the potential to be able to take off really steeply and to be really quiet.