Does the case of the Montana doctor who falsely treated multiple patients for cancer prove wrong the idea insurance companies help keep costs down?

Starter comment: So falsely treating patients for cancer is the only the tip of the iceberg for this guy. He likely indirectly killed at least one of his patients because of unneeded chemo, likely euthanized another patient against their will and was essentially a pain pill clinic for many others. All of this leads to me think the following. This guy was in practice for more than a decade, and during that time treated 4 times as many patients as the median oncologist despite living in the lowest population density state and was prescribing huge amounts of pain medicine. He often had no proof of cancer, not even conducting biopsies. If insurance is unable to identify this amount of blatant fraud, then doesn’t this refute the argument that insurance actually keep costs by stopping unnecessary treatments?