Literally, the CDC only mentions two primary sources of lung cancer: smoking and radon. Unless you have an unusual, alternative risk factor, it's practically correct to say eliminating smoking and radon prevent lung cancer.
I think it's a mistake to conflate an infinite number of hypothetical risks with a definite and known risk. It leads to analysis paralysis and FUD. It is not possible to know what, among all of the infinite hypothetical options, is the best to reduce your mortality. So let's focus on the concrete steps we can take and that we do know are effective.
For most people, that is not radon mitigation, because most people don't have a radon problem. If you find out that it is a problem for you, and you have the cash to solve it - just solve it. It's that simple.
Enjoy one free beer a month, dude. Chances are you won’t develop a vicious cancer.
If you own a home in such a locale, you might as well do any mitigation while living in the house. Otherwise you're not getting any cancer risk reduction for your dollars but you'll still pay those same dollars for the mitigation when you sell the house.
We pay to live further from the toxic waste dump, the motorway or the pylons. We want filtered water. We want clean air. We pay to have nicer, less risky things.
If in 20 years I find out I got ripped off, I won't really be upset about it.