> If $4700 in ads could sway an entire US Presidential election

That's a little disingenuous. IIRC, Facebook identified at least a $100k more on its platform, and they permitted finer-grained targeting than Google.

You're right that it's hard to believe stuff like this tipped the election outcome, but it's not impossible that it did. The sales pitch of targeted online ads is that they're cheaper and more effective than mass-market ads. Also, given the way US elections are conducted, the right pressure applied in the right areas could deliver an outsized effect on the outcome. Taken together the amount of money needed to sway a close election could possibility be less than one would expect.