I don't think the courses are math-heavy. In fact, the students from the economics faculty look down on RSM because of the lack of math in business administration.
However, the courses are very academically focused. I've heard from friends at other schools in Europe/US that they just make case studies and reports all the time. RSM professors focus on getting their students in contact with their field of research by letting them read up on all kinds of scientific stuff. Can be pretty boring, but in the long run it does stimulate critical and analytical thinking a lot more than other teaching styles.
It's true that there are a lot of Germans students around. No one's really proud of that, but hey, what can you do about it?