Physical exercise is, probably, important - there are some studies that suggest diet is far more important in our health (as opposed to fitness) than exercise. Whether it's the 'most' important is questionable - is it better a life to be eminently employable and die at 65 or minimum wage but fit until you're 90?
Someone on the minimum wage is most umlikely to be fit until 90, and there is no reason why someone with a desireable job and a reasonably high income should die in their 60s: the job may be sedentary, but they will have the education and intelligence to know the value of physical and mental exercise, and be able to eat a good, balanced diet.
As to the idea that there is no educational value in games but an intrinsic education value in books I'll pitch the historically well-informed and elucidating Assassin's Creed series against, say, Harry Potter or Lord of the Rings (both of which, to be clear, I'd heartily recommend).
There are lots of books not worth reading, and some downright harmful ones, and there may be some computer games with some educational value, but it remains true that, broadly speaking, books, and traditional, outdoor play, are better than computer games for kids.