Earlier quoted context omitted.
So when its raining hard and you have to stop quickly and safely? will that 100$ bike be as good/safe as a sensible entry level MTB say 800/900$ with properly setup brakes?
The cheap ones are usually bought used anyway and might need repairs, you're free to upgrade the brakes. I'm usually limited by road traction, not my brakes, though, and they're as cheap as it gets. Proper maintenance is more important than expensive components.
Also not every where is SF with its balmy climate try riding where it rains a lot where stopping in the wet safely is probably more important