Early electric motors were awful, because there was no good way to control their speed.

For example, DC motors used in some late-1900s trains still had a giant variable resistor in series with their motor, burning away a huge chunk of the power as heat to force the motor to run at a lower speed during acceleration. AC motors weren't much better.

Electric motors only became truly efficient when variable-frequency drive became viable, which was in the 1980s due to semiconductor innovation.

Surely the variable resistor would only have been on the field winding. It wouldn't waste that much energy.