Hi,
I'd say ON/OFF has nothing to do with feedback. It is the control method....how the load is beeing controlled.
ON/OFF is some kind of digital control method... In opposite to an analog control mechanism.
PWM is a fast ON/OFF control, withing the load with a triac or SCR is ON/OFF control, too.
******
PID is the calculation method, the algorithm...how to calculate the new control value.
The control value for an ON/OFF control can be the duty cycle.
Klaus