Well, your circle of knowledge is limited. Chemo does kill cancer. So does radiation. There will be side effects but many people have had years added to their life instead of certain death. I know this from my direct circle of knowledge.
My brother died cancer free. They kept him on BP meds even though his pressure was low and he peeled over and died. So yes, the chemo killed the cancer, but the patient died, probably from the chemo treatments. But at least he was a “success for the Doctors stats - he lived 5 years.