> the number of people manually overriding fonts isn't even a rounding error. It's not even a rounding error's rounding error

This is very obviously true. And given the fact that 100% of mainstream websites and 99.99% of non-mainstream ones use font declarations other than “serif”, “sans-serif”, or “monospace,” it is absolutely unsurprising that no one (but us super nerds) bothers to set this setting that every website will override.

And indeed, the near-universal usage of web fonts today has taken us even farther into the territory where a web property specifies the precise appearance, leaving no decisions to the user agent. If it weren’t for responsive layouts being standard, the Web would have more in common with a PDF than the early HTML web where users might have a reason to use user stylesheets and specify their preferred fonts.