An excellent way of looking at things. I agree.
I have also not found any MB that had lacking brakes. Okay, my 16V chewed them up bad, but we're talking about a race-track weekend. I have no idea of why anyone with a 190E would need 600SL brakes.
Our C36 had much larger brakes than the C280 that the car was based on, but all the braking components were upgraded in some form or another.
The C230 has smaller brakes and less robust components, but is much less capable of generating such speed in such a short distance. That said, the C230 is still capable of outbraking most "regular" cars on the road.
If I owned an E420/400E, I might consider tires before brakes. The braking power of my C230 when I was running S-02PP's on the car was shocking due to the adhesion of the tires. This didn't help with race-track durability, but for "panic-stop" braking, big brakes don't do a durn bit of good when tires can't grip.
Now, if your car is upgraded in the power dept. then you should talk to an expert. And not about "parts fitting", but about a real braking solution for your car. When I was racing we called it "make it right from pedal to pads."
1998 C230 "Black Betty"