There is reason in that thinking., but focusing on series, rather than parallel or series parallel, I can also see that side of it. since all power is distributed as electricity to the traction motors not through a power splitting arrangement. At least in transportation, I've generally heard that referenced as (almost all locos) D-E, often on cars, trucks, and buses, add batteries get DE Hybrid (available in both series and parallel, as in BAE vs Allison drives for buses) delete diesel, get B-E (like a Proterra)