> Most of them are awful but only in rare cases do they cause permanent damage beyond what is already happening with the cancer

That's simply not true. Chemotherapy, in particular, is ridiculously bad.

Chemo brain is a thing. Another example, people have to wear cold packs on their hands and feet in order to minimize the neuropathy that some chemotherapies can cause. Other chemotherapies cause your veins to leak with attendant swelling everywhere. Several years after therapy, some of that swelling still persists. Radiation is horrendously bad at damaging intestinal tissue. etc.

Yes, it beats being dead. That's about all you can say about it.