Boltar ) gurgled happily, sounding much like they
were saying :

Don't forget that the engine is basically just being used as a
generator, therefore can run at optimum revs for the specific output
- there's no requirement for any kind of useful rev range or torque
curve.

True , and I suppose that will mitigate it somewhat. However
ultimately that engine will produce less power than a normal bus
engine so when relying on the engine alone its going to be slower
compared to the normal engine running at optimum gearing.

shrug
How often do bus engines require full power? Not very.

Don't forget that one thing electric motors are very good at is producing
large amounts of torque from rest.