Yes every cancer is different, responds to different therapy, and with different survival rates. However, cancer treatment, as a whole, works. Oncologists do not prescribe incredibly intense treatments like chemotherapy out of nowhere. Chemotherapy is often not curative. Instead, it's used to both prolong life and improve quality of life.
Dying from late-stage cancer is often painful and miserable. It might be shocking, but getting just a few more months from chemo can provide a greater quality of life. Keyword can. Every oncologist is different with different recommendations, and they explain the risks very concretely. There is always an option to refuse treatment, but bear in mind it's not just about how quick you die. It's also about how much that dying sucks.