[NeilBlanchard]

The losses of the generator are more than offset, I think, by the fact that the engine runs at a single RPM - right at its peak efficiency, all the time. No idling either.

Also, if the engine has to move the vehicle by itself, then it has to be powerful enough to meet the peak torque required; whereas in a genset, the battery can be a buffer, and the engine only has to meet just above the average torque required plus the losses.

Being a smaller engine, it can warm up faster, and the cooling system can be proportionally smaller, the fuel tank can be smaller, and the cooling system will have less areo drag, and it can be closed off when not in use. And a serial/series hybrid avoids the need for any multi-gear transmission or clutches.

Typical plug to wheel losses are about 15%, by the way.