Electric propulsion must deliver the required shaft power without allowing motor, inverter or cooling mass to erase the advantage elsewhere in the aircraft.
Mass compounds
A heavier propulsion system needs more structure and more energy to carry it. Small improvements at component level can therefore create larger gains across the full aircraft.
Power density is an aircraft-level design variable.
Heat is part of the machine
Motors and inverters can be highly efficient, but the remaining losses still become heat. Cooling must protect performance without adding excessive drag, mass or complexity.
Thermal architecture belongs inside propulsion design from the beginning.
Design from the mission backwards
Start with required thrust, flight profile, reserves and installation constraints. Then define machine speed, voltage, cooling and energy architecture around the real aircraft.
This keeps technology tied to useful flight.
Better power density gives the whole aircraft more freedom.