Control valves for waterjet systems, control-valve actuators, waterjet systems, methods for operating waterjet systems, and associated devices, systems, and methods are disclosed. A control valve configured in accordance with a particular embodiment includes a first seat having a tapered inner surface, a second seat having a contact surface, and an elongated pin having a shaft portion and an end portion. The pin is movable relative to the first and second seats between a shutoff position and one or more throttling positions. When the pin is at the shutoff position, the end portion of the pin is in contact with the contact surface. When the pin is at the throttling position, the end portion of the pin is spaced apart from the contact surface and the tapered inner surface and the shaft portion of the pin at least partially define a throttling gap.