Maybe you need to readjust your image of what happens. If it isn't for the vigilance of the people all of the above can happen. They happen in other countries. Corruption of those in powers is a constant in the world, Germany is doing okay now, but it just takes one blink and things can go bad - as they have in many other countries throughout history.

Yep, politics is the key contribution to our intellectual dark ages.

German prosecutors are not independent but have to follow the authority of the ministry of justice. So in principle, politicians can stop the prosecutors. They would rarely do so as that would be the bigger scandal in the end.