If you can lock the wheels up, the brakes are good enough. Obviously modern cars have ABS to prevent this, but the point stands: brakes can only be *so* good. Unless you start fitting parachutes to the car.
The single most important safety item on any car is the tyres. If you put shitty £10 teflon tyres on then your grip levels are compromised, and braking and cornering (including swerving) will all be far below safe levels.
Summer tyres are practically worthless in snow or ice. Winter snow/ice tyres are subpar in dry summer conditions. Cheap tyres with shitty grip levels mean you could lock up the wheels just using your handbrake. You want the right tyres for the conditions, and you want the best grip available because that is the safest configuration available.
I've had sports vehicles that could lock the wheels up using "performance summer" tyres, but that could not lock up the tyres running slicks on track, no matter had hard I stomped the pedal. The more grip that is available, the harder the brakes are able to work.
It's all about the tyres ;)