Interesting topic, and funny that I personally consider the text width and font size of danluu’s blog to be a “bug”. It is well known that we can read faster with narrower text columns (remember newspaper columns when they were printed on paper). This is why I always read this particular blog with Apple’s Reader mode, which renders the text using larger font and narrower width.
There is no CSS configuration for text/font on the website, so it's using browser defaults.
Seems like reader mode is needed due to bad defaults.
That's a cop out in this specific instance: he knows the defaults are a bug, he can change it with maybe 2x lines of CSS, but he is blind to the fact that it's a bug.
After all, he is complaining about the defaults in other software, but he is blind to the defaults he presents the user.
There is no way to specify a good size in CSS - a size that looks good on current computers will be too big on old computers, and a size that looks good on old computers looks too small on current ones. Browsers and users are the ones who can fix this.