The SF salary is high because of high demand and low supply (of competent engineers). If you move remote, you increase the supply of competent engineers (there are likely people in middle-of-nowhere that are just as good as SF engineers but don't want to move because of other reasons - hence market inefficiency). Since you're increasing supply with the same demand, now the SF salary is going to drop (and establish a new market clearing price with the new supply & demand dynamics).
I think in the long run the SF salary (for the average developer) will be a historical anomaly in a place and time - kind of like the California Gold Rush in the 19th century.
(If your argument boils down to SF having more strictly more competent engineers than other places and that being the cause of the pay discrepancy, I strongly disagree)