I know someone who smoked a pack her day her whole life, and died at 90 while remaining in good health for the age the decade before.

I know someone who never smoked in his life and got lung cancer at 52.

Does that mean anything? Should we now conclude that smoking prevents lung cancer?

Quality of life, health, remaining lifetime, sickness progressions are all very complex interactions. All you can do is what happens on average, and play the odds based on that.