When you make 50 million in one city alone, you are very active and pretty powerful in my book. I don't think the Turkish gangs in Germany make this much. Mahmoud Al-Zein is also regarded as one of the most powerful crime bosses in Germany, by the public as well as by the police. So yeah, these guys are big time.
As for homegrown OC in Germany, never underestimate the German Hells Angels. They are really powerful and they even had a personal death squad in Kiel involved in the torturing and murder of rivals. That's pretty effed up lol