The truth is that there is an incredible amount of hard science which is actively expanding our knowledge of how to best train the human body and push the limits of performance, endurance, and strength.
While it is obviously true that scientific advances at the “high end” are showing quantifiable results, it’s harder to ascertain whether the everyman/woman is benefitting, because of so many confounding factors in culture, lifestyle and such. Otherwise we would all be walking around like Greek gods/goddesses with our newfound knowledge.
It was that long ago that weight lifting was shunned by athletes because “bulking up” was thought to lower performance.
Pretty much everything in a modern gym was designed to allow more efficient or lower impact training of any particular body part or system.
If what you’re saying is that we haven’t found a magic pill to bypass the physics of metabolism and muscle growth, certainly this is true. But there’s a lot more out there than just trying to find fancy new packaging, marketing, or gimmicks to sell to people.
Even if there were no improvements at all we would expect this for no other reason than the statistics of an increasing population of athletes and our effort to pick out only the far right tail of the distribution.
Having said that, nutrition is just better now, for almost everyone, compared to the ancient Greeks. So you would also expect more athletes to come out of today's society than you would back then.
the innovation is in pharmaceuticals.
Basically I'm saying you can get all the exercise you need for general health given a landscape with varied terrain and some imagination; or a barbell, weights, and cage (which will cost <$1000 and last for 20 years); or with other basic tools like gymnastics rings. We don't need fitness fads---but people like them for various reasons. And that's fine.