I've also had two cars lose brake pressure. I'm very thankful that the cable-operated parking/emergency brake was functional on both cars; it saved one of them from going through the back wall of the garage.
The cable-operated E-brake definitely doesn't stop the car anywhere near as well as the power-assisted hydraulic brakes, but having two different braking methods can be a literal lifesaver when one system fails. (And all systems fail! I'd previously had two other cars where the E-brake didn't work.)
I've never had my breaks fail on me. I also don't use the parking break that often. I would be so proud of myself if I realized what was going on, remembered that the e break exists, and used it before hitting the back wall of my garage.
When the hydraulics failed (brake line exploded) on my old vehicle I discovered that the cable is also attached to the brake pedal, so I didn't have to play games with the parking brake mechanism. There is a world of difference in braking force though, it's like pushing on the side of a brick building to gently encourage the vehicle to stop. I was lucky that I was driving a manual so I could also downshift to kill the speed.
I had the engine fail (timing belt broke) and that also killed the hydraulics in that car, very different behaviour of the brakes compared to normal and you need a hell of a lot of pressure to stop but it still works. Downshifting was not an option since the engine didn't work anymore.
You are probably referring to the brake assist mechanism in all cars after the 90's. It uses vacuum pressure from the engine to help you push the pedal down. Without the engine running, the brakes will work ~3 times, and then they'll get super hard to press - but they will still function if you have leg muscles strong enough to work them.
The cable-operated E-brake definitely doesn't stop the car anywhere near as well as the power-assisted hydraulic brakes, but having two different braking methods can be a literal lifesaver when one system fails. (And all systems fail! I'd previously had two other cars where the E-brake didn't work.)