Do you really believe your third point? That most medical interventions for cancer do not prolong life? Or the word necessarily means your argument is null like "not all interventions prolong life". Yeah , we knew that already. It's never 100%.
I actually do and most of it based on what I have have directly experienced with what, especially older doctors, counsel their patients.
There is a lot of literature on how doctors die [1], which also drives my beliefs.
I am also influenced and how weak the statistical significance is on evidence based literature on interventions and how often the interventions are difficult to replicate.
As always, please do your own research :)
1- https://www.thehappymd.com/blog/bid/295228/how-doctors-die
Specifically, medical interventions for cancer AS A RESULT of some types of screening do not prolong life.
Medical interventions for symptomatic cancer, and some types of screening, certainly do prolong life, and quality of life.
There are so many confounding factors in this it's hard to do something like a pareto breakdown, but it would certainly be interesting to see.
But that was 20 years ago. He lives a normal life now and has a family. I'm pretty sure chemo was worth it.