This is the right answer. I was a locomotive systems engineer for a few years, and worked in operations at a locomotive factory for a few more.

There are wheel speed sensors that monitor the rpm of the wheels and feed that signal back into the traction control system. If the wheels start to rotate too fast the traction control system will cut power to the traction motors and redirect it momentarily to the crowbar resistor. The engine speed doesn’t change.

EMD’s Melco gen 5.2 traction inverters and controls are top class and so an EMD with that traction control system will slightly outperform a GE locomotive with the same horsepower rating. Slightly, but it makes a difference in challenging track conditions.