I'm not arguing for any particular "narrative" although you seem to be.

You seem to be suggesting that more criminals behind bars leads to lower crime. Is there any evidence that this is true? Could this be a coincidence, or could there be some other factor lowering crime? Are you jumping to conclusions based on your own favorite narrative?

The OP similarly lists two facts and then jumps to the same conclusion: Crime rates have plummeted, and we are all much safer than we were decades ago. (Therefore) our incarceration system working?

I think to make that claim one must "show one's work".