Based on the comments above?
If the CX brake system was weak and unable to create strong pressure then the wheels would not be able to lock up and so the ABS would never kick in. Given the comments from several people saying the system felt soft on the pedal and reports of pressure fail it would make sense.
Do we know if it is fair to say they underspec'd it or was the volume of components that arrived following the prototype being below spec? I figure they gave the prototype a good hard run a few times before they said yes. It's not like the factory team don't enjoy a good drive?
I follow a Mini forum and find the discussion around the installation of "track" discs & pads humorous. They spend ages discussing which uprated road/track pads to fit then, once fitted, moan about the fact that they are dead, noisy and numb. Before they had them fitted did they ever find the pedal hit the bulkhead? Do they really brake that late and hard?
I have fitted uprated discs and brakes to the ML63 as it weighs 2+ tonnes and I have felt fade a couple of times when in a rush. EBC are among several good vendors making aftermarket upgrades for the MB. Given the standard brakes are Brembo it's quite a step to improve things. So it has EBC uprated front discs and Yellow Stuff road/track pads plus uprated Brembo discs and Yellow Stuff pads on the back. When they are cold they take longer/harder to stop the car from any given speed. So the uprated bit is not really an improvement for the daily traffic. If I am pushing the lorry around Basingrad roundabouts on a clear day they are brilliant once warmed through. I am only surprised that the front spoiler does not have scrape marks on the bottom given how well they work when up to temp. So the benefit is only really seen in extremis. You just have to be aware of what you are looking for.