That is a very good point.
> Also very interesting, and counter to the usual narratives about health. (Everything is heritable...)
And yet this need not lead us to the conclusion that self-improvement is futile. Consider the scenario where diet is highly heritable and also extremely important to health outcomes. If people could be convinced of the latter, they would, to varying degrees, improve their diet and therefore their health. After smoking was tied to lung cancer, I imagine that people (at all levels of genetic predisposition to smoking) greatly reduced the amount that they smoked. Smoking levels could have been 100% heritable both before and after the revelation, but would have been reduced over time.
> 5. fat percentage: -3.3 (!)
I'm not sure why you singled fat percentage out as the least significant (in the colloquial sense). The -3.3 is a reduction from 24.0, so the percentage change is ~14%.
> 2kg of weight? I fluctuate more than that on a weekly basis...
To take your quip seriously, I don't think this is a good comparison. If a specific intervention increased lean mass and decreased fat mass by equal amounts (say, 10kg), it would be highly beneficial and yet count for absolutely nothing with respect to BMI or weight. The specific changes cited here are 1.4kg lean mass and -3.3kg fat mass. I would actually count that as a 4.7kg improvement!