Judging from the author's other assertions, this suggestion probably comes from a place of not limiting yourself to system fonts given that they're so prevalent. I can't say I agree either, and would add that some of the "free fonts that inundate the internet" are professionally designed by well-respected foundries.

That said, perhaps we should view these "rules" as laying a foundation for people who know nothing. I see the equivalent in fashion all the time, where breaking the standard set of fashion "rules" without knowing them in the first place can lead to disaster. Only by internalizing the rules can you then subvert them successfully.

Yeah IIRC he has a page elsewhere listing system fonts and proposing alternatives, including several free fonts. I'm pretty sure the reason is just that free fonts tend not to be "full featured." His typographic style is based on classic printing, so it really depends on the font having features like small caps, tabular, lining, & proportional number options, etc.

This is the list: https://practicaltypography.com/font-recommendations.html

> "That said, perhaps we should view these "rules" as laying a foundation for people who know nothing."

Well, I am one of those people. I have never earned a dime as a graphic designer. Never even completed a MOOC or a regular course in this subject.

But I do take presentation seriously, and meddle in fonts, colors, design, etc., and have designed friends' wedding invitations, greetings cards, and so on. I also took typography seriously when turning in college assignments, my Master’s thesis, etc.

Even to a sub-rookie like myself, I simply don't agree with that point. And when two of ten minutes go to a point that I simply find wrong, I think it should be pointed out loud and clear, and it reduces the value of the list significantly.