No, it isn't. Your claim is "punishment as a deterrence is dead".
I am claiming that:
If the punishment for murder is 20 years in prison, there will be X murders per capita. If the punishment for murder is nothing, there will MUCH more than X murders per capita. How much exactly? I don't know. But I know damn sure there will be a lot more.
You can have a real debate about where the point of diminishing returns and how it models. Is it linear or does it decay exponentially? Is one year sufficient or does it take five or ten?
You come here with a bold claim like "punishment as a deterrence is dead". It absolutely, unequivocally is not. If you want to have a more nuanced conversation, you need to make a more nuanced claim. Because the one you made is ignorant and obviously false.
The question is whether harshness and cruelty themselves are deterrents, or if a humane rehabilitation scheme would do better at reforming murderers into non-murderers. The evidence suggests the latter.
Much of crime is a matter of impulse control. Most people don't do a cost benefit analysis, weighing the odds and severity of punishment. They get angry or greedy or whatever and they act.
I wish I could find a video where a specialist in criminal rehabilitation says that most of the guys he works with ruined their lives in 10 seconds, with just one bad impulsive decision.