So you accept that regular exercise is useful for understanding the physiological implications of the diet, but you question whether regular exercise is healthy?

No. I believe there is such a thing as excessive exercise, which I feel is what the post was describing. While under and excessive excessive your body will be stressed enough that it should be easy to see the effects of your diet, and so it would be relatively easy to optimize your diet for such a regime. But the diet that such a regime requires is not necessarily optimal (or good) for people with a more reasonable and healthy lifestyle.