Just a little anecdote: I remember when I did my driving test the guy asked me for the location of the “emergency brake”. I had never heard that term before and had to think for 2 seconds and pointed to the parking brake. Turns out my guess was right.
That being said: The parking brake slows down the vehicle a bit but not much. In your experiment you should have shifted down substantially to 1st gear and THEN applied the parking brake. In that case it should have enough power to stop you.