What is inside the "trigger" of a DC drill switch
According to comments: YES, that's all.

The thread linked to by nick-alexeev mentions that at the end of the 'trigger' pull, full power is connected directly, bypassing the PWM driver and MOSFET for efficiency - that may explain the 'on/off" behavior on low voltage, as a logic-level MOSFET still seems less likely, at least on >9.6V drills.