Comment by Animats

Correction: lower OFF resistances, higher ON resistances. There was heat generation even outside the transition period.

Every modern locomotive motor is powered by a switching power supply. The transistor packages are about 10x20cm. You could hold one in your hand. They're not super-expensive. They're smaller than a mechanical switch of the same rating.

MOSFETs are insanely good switches. It's amazing that's physically possible.

[1] https://publisher.hitachienergy.com/preview?DocumentID=5SYA1...