The study doesn't show that donation is a good thing. Showing a miniscule reduction in blood markers is not the relevant variable - what you'd actually care about is: do I liver a longer or better life because of this intervention? There simply isn't any evidence that a tiny reduction in PFAS from blood donation results in any improvement in any clinical outcomes. Because we don't know either way, it's also possible that there would be harms from this - as blood donation is not entirely risk free, exposing people to syncope while driving after giving blood, skin complications like infections, or other rare issues we don't even know about.