How much worse are the bad ones than the others?

I don't think they mean you never actually use the brakes.

That person is probably referring to the Tesla feature where when you don't use the gas pedal, the system is slightly recharging the batteries all the times (via magnets). You can turn this off if you don't like it. Then you get used to a driving style where you take your foot off the 'gas pedal' before you need to stop and the car slows down on it own (through regen braking), and so the 'UX' is you just selectively apply the gas pedal or not to go fast or slow down. If you need to stop suddenly you use the brake. It's an automatic thing after a while, you don't need to think about it. I sometimes have to get used to a 'regular gas car' that doesn't have this when I drive something else.

I have a Tesla, and I can assure you that I use the actual brakes crazy less than a normal car. I do have the AWD version which I do believe has more regenerative braking than the RWD model. Generally if it's a "oops I messed up" and you see a red light or stop sign later than usual you tap the brakes. But even on pretty steep hills I don't hit the brakes and basically never ride the brakes which was pretty common on my subaru.

The answer is that an electrical motor can also be a generator. An electrical motor when a current is applied causes it to rotate. When power is drawn from a rotating motor it generates a counter-torque proportional to the power extracted. Not perfectly efficient of course and there are still resistive and inductive losses but that means less energy dissipation by friction. This synergies beautifully with an electrical power system in boosting overall efficiency.

Imagine a generator on a bicycle, you pedal to make a light bulb light up. There is of course inherent friction in the system, but a large fraction is actually pushing magnet fields around to produce electricity. That part actually has no friction, while it's not 100% efficient in the form of stray magnetic fields and some heating, normal metal on metal friction is a very small fraction.

Normal brakes use 100% friction, which of course causes substantial heat, and increases wear and tear on the pads, the rotor, and brake fluid. These type issues are why it's often recommended to use a lower gear down hills so you can offload the brakes with engine friction.

So not only does regenerative braking produce less dust, but it produces less heat, and the brakes/rotors/fluid are on average cooler and in a state where any needed braking causes less wear.

You apply a load across the motor, the same way any electricity is generated.