I have read every article that has hit HN's front page. It seems like at least one per month since I joined in the heat of COVID at which point in time HN was adamant that bolus doses of vitamin d prevented COVID...
Each and every article leads to the same conclusion for me though - people should really be asking an endocrinologist instead of Dunning–Kruger-ing their health.
Let me get this straight: the source of your expertise on multivitamins and vitamin D is HackerNews articles, which makes you more qualified than the average physician, and you're accusing others of Dunning-Kruger?
As per the research, what vitamin D did, if an optimal level, is prevent mortality from Covid, not prevent one from getting Covid. I don't recall any basis for claims that it prevented Covid.
Doctors are utterly useless when it comes to vitamin D. They don't even test anyone who doesn't beg for it. They also never help optimize anyone's level.