If you honestly compare Germany and the US, you will notice that the prevalence of rape is much higher in the US (US: ~43/100k vs. Ger: ~15/100k, source: statista.com). Comparing gang rape specifically is more difficult though, because the US doesn’t seem to keep track of that (or at least i couldn’t find absolute numbers). According to Wikipedia 22.8% of rapes with female victims where gang rapes. That makes ~9/100k in the US vs ~1/100k in Germany.
Then again I don’t think statistics regarding a lot of crimes are easily comparable. There might be differences regarding underreporting and legal definitions that skew numbers in different ways.