Not on mine. I have a SOHO ONT where the battery and
power supply are integrated together in a separate
and very large external box (it has 4 batteries).
When I pull the power connector plug from the
ONT it's 100% disconnected.
The regular home ONT, you are correct, that is the case.
There is no reset button on the SOHO ONT, you have
no choise but to pull the power plug.