Are you intentionally confusing prophylactic use and acute treatment? Or don't you realize that there's a difference between taking something to prevent an illness, and taking something to cure one after it's underway?
Very few of the studies on treatment of acute Wuhan Flu with HCQ have published their dosage. Two studies were doing 600mg on the first day and a lower 400mg maintenance dose after that, presumably as an acute treatment, not as prophylaxis. That's actually lower than the acute treatment for malaria, which starts at 800mg and goes to 400mg the next several days.
Right now, all the prophylactic studies for the Chinese virus are still in the preclinical stage, but given there's a very low risk to taking it at prophylactic doses, and the anecdotal evidence from actual doctors using it to save lives is very positive, it's entirely prudent to take it if you have the means.