Soft brake pads are standard on most new cars and are basically a scam. They give a great soft pedal feel and will stop the car on a dime and give you 9 cents change. But, they don't last. I live in S Texas where we drive many more miles per brake application that people do on say the East Coast. I can easily get 40K miles out of a set of pads and double that from rotors.
Go to a harder brake pad, don't ride your brake pedal, and don't stop hard. And above all don't get your brakes done at the MB dealer. Does fuzzy end of the lollypop ring a bell?