Agreed that life is not that simple as a math equation, but I think baselines apply, e.g. if you are sedentary, adding 150-180 mins of moderate exercise will definitely improve your health and life.
if you are already meeting that baseline, and still have issues, then you should look at tweaking other variables in the equation, whether diet, stress, etc.
What I find worrying is the cherry picking some people do, e.g. "aha your body will get used to exercise, so I might as well not bother", then wonder why at their next visit to the doctor, they are now told to go on a steady diet of statins etc.
