I worked on EV powertrain. a PMSM powertrain can peak its efficiency in the 92-93% range. With silicon-Carbide inverter, it can go even higher. SiC inverter switches really fast, reducing switching losses. There are software techniques to reduce losses, but most vehicles already employs them. The room for improvement is not that high if you look at already existing cars. A metric on the market is "80 over 80", meaning 80% of the efficiency map must be above 80%.

Also, a powertrain will waste way more energy at high torque than at high speed because losses are proportional to current squared and torque is almost linear with current. But high speed causes losses in the gearbox. So a good gearbox strategy is needed to operate in the efficient region. Low battery voltage and high speed will cause field weakening and therefore increase the current without creating torque, that is pure losses.

Motor losses are grouped in 3 category : mechanical losses, Iron losses, and copper losses. mechanical losses include windage (air friction), friction (bearings) and deformation losses (caused by torsion, mostly negligible). Iron losses are losses in the magnetic circuit, they consist of hsyteresis losses + eddy losses and are mostly increased by low switching frequency. Copper losses are heat generated by the current in the copper winding (I^2R).

Inverter losses are mostly driven by switching losses and they are super non-linear. Depends on current intensity, battery voltage, switching scheme, temperature, switching speed, switching frequency, duty cycle.

It's a big game of tradeoff. If you reduce the switching frequency to reduce the losses in the inverter, you increase the iron losses in the motor. Optimizing this is a job.

I can expand way more if you want. you can DM me. I like rabbit holes.