I disagree. I think if you took a reasonably fit marathoner (approximately 3:30 time on a flat course) and compared them to someone who only does mild exercise every day, the marathoner will come out as far healthier.
I think this because to be even a mediocre marathoner, one needs to exercise with about the same frequency as the control person. But one also needs to work diligently on a large peripheral system like flexibility and mobility, recovery routines, stricter diet controls such as counting calories, macros, ensuring proper vitamin/mineral uptake, strength work with lifting, etc.
Sure, a mild exerciser can be relatively healthy, but the real difference is that the marathoner has challenging goals to accompany the systems for building health; whereas the mild exerciser only has the systems and easily accomplishable or even no goals besides "being healthy".
Don’t forget the wear and tear on your body. Not many people can maintain marathon training for a long time without injuries. There some that can but those are only a few. I have seen the same in martial arts. Once you reach 40 the injuries start accumulating.
I think this because to be even a mediocre marathoner, one needs to exercise with about the same frequency as the control person. But one also needs to work diligently on a large peripheral system like flexibility and mobility, recovery routines, stricter diet controls such as counting calories, macros, ensuring proper vitamin/mineral uptake, strength work with lifting, etc.
Sure, a mild exerciser can be relatively healthy, but the real difference is that the marathoner has challenging goals to accompany the systems for building health; whereas the mild exerciser only has the systems and easily accomplishable or even no goals besides "being healthy".