It appears that corruption in Germany is mostly high-level corruption. It's super unlikely that a cop will say "I can make this speeding ticket go away if you donate to our fundraiser", and you won't see an average family speed up building permits by handing over stuffed envelopes, but the elite in industry and politics seems to be comfortably close.
The Berlin rent control was just a cover up rent for some stupid mistakes that were made in the past. It's basically a bribe to the public. Oh, we sold government owned housing to private investors? Here, have some forcibly lowered rent payments. Of course they rushed the bill and it was overturned.
If the greens can somehow figure out how to avoid falling into these self inflicted traps they would be strong enough to stand their own, as it is right now they still need some common sense beaten into them. My hope is that they do their big government investments, let the economy recover and then either become a boring government party or stay a quirky opposition party.