Still, the scale of the two issues - prosecutions vs platform censorship basically implies that most of the things being censored do not rise to that level of illegality.
Yes, the new thing is basically that the platforms are taking part in the enforcement. This provides a pragmatic and efficient solution:
* The illegal content can be removed quickly, without tying up resources in the prosecution of minor offenders. Prosecution can focus on the worst of them.
* The platforms get to play the role of a neutral party and are not themselves being responsible for distributing the illegal content.
Given the increased centralization on the Internet to a few of these platforms, this allows for efficient implementation of the law.
This is quite similar to the development of copyright law (in the US). The DMCA grants platforms immunity by actively taking part in the removal of illegal content when requested. I haven't checked the numbers, but I expect that here also the number of DMCA takedowns greatly outnumbers the copyright violation law suits (which would be kept for the worst offenders)
Your portrayal of NetzDG as "[allowing] for efficient implementation" is IMHO very naive. NetzDG has been highly controversial in the informed part of the populace (for example, it's frequently discussed https://netzpolitik.org, in German). Among the concerns are that providers preemptively take down content outside the regular juristical process without transparency and appeal. Moreover, the law is criticized for cementing the defacto monopolization on the Web, and has yet to stand before court. It is seen as a publicity stunt to "do something about hate speech and fake news" and has had also the smell of an attempt to suppress opposing views when it was signed just during last year's federal election campaign by Heiko Maas, former minister of justice, now minister of foreign affairs.
Still, the scale of the two issues - prosecutions vs platform censorship basically implies that most of the things being censored do not rise to that level of illegality.