Citation needed. Never heard of any differences in fees for foreigners.
> Then they hardly get access to the public student dorms
Not in my experience. Dorms are full of foreigh students.
> and are put 3-6 people in old, unclean apartments far away from university (partly without public transport access)
"Are put"? What you describe is a "WG" ("Wohngemeinschaft" roughly "living community") which is simply a co-rental. So nobody "is put" there, you search and rent what you can find. WGs are generally recommended for foreign students because it allows better socializing and integration.
> EACH of them pays as much as a German would pay for the whole apartment
What you state is that a foreigner typically pays 3x-6x compared to a native, which is false. The price for 1 room in a WG is normally somewhat lower than for a 1-room-appartment.
> Old dudes (teachers, profs, organizers) dating barely legal girls in exchange for favors also is accepted practice.
University typically starts at the age of 21-23. Since you call this "barely legal" this points out that you either not know what you are talking about or intentionally make false claims.
I live and work in Germany since 2001, I've worked as a researcher at a university institution 2001-2004 and knew a lot of foreign students, also as close friends. Your post is not compatible with the reality that I know.