Gentrification is a problem, but long time renters in Germany are really having it good. An example of how does the system works here: I pay twice as much as some German friends living in my district because my parents didn't sign me up in a union 20 years ago. I'm OK with that, it's the game, but refusing new buildings/companies to keep the rents low is BS.
Kreuzberg is very well located, Berlin is huge, time to accept that 1989 was a long time ago.