Let me just say this... any time we've reached the point where actual design notes are being cited as the "guidance" needed to be provided for absolute beginners to start running a ttrpg... I just... yeah I don't even know what to say to that.
Have you had math or science classes, where you were just
given some random formula to plug-n-chug, without any explanation as to where it came from or why it mattered?
I've dealt with classes like that. Thankfully, I avoided most of them, but there were a couple I simply couldn't avoid. Those classes are often worse than useless for actually getting students to
learn, as opposed to briefly memorizing something solely to complete tests.
Now, I grant that some of the time, an actual, full-throated, rigorous explanation of
why a particular thing is the way it is could go over someone's head, or require things they don't know yet. One of my go-to examples is the logistic function (the "sigmoid" curve, which we have all become so frustratingly acquainted with as a result of the pandemic.) That's the one that looks like a squashed S, and represents a population growing from an initial state up to a maximum carrying capacity. To
truly understand why that function exists--and why it
must be what it is, and that no other thing would do--you have to take differential equations.
That is what I would call "designer's notes."
But you don't need to take four years of calculus in order to get the fundamental idea of why it works the way it does. You can, instead, give practical and physically-rooted explanations. You can have students work through in an investigative kind of way, and then show them in practical terms how this function does the job.(Briefly, it grows both based on how many things there are, and how much more "space" there is for more things to grow. If there are few things, it grows slow; if there is almost no "space" left for new things, it grows slow. It only grows fast when there are lots of things
and lots of space left for new things.)
That's how I see Heinsoo's and Tweet's commentaries here, as well as their "Game Master" asides and such. Particularly the third example. They aren't teaching game design. But they are giving people a
reason for why
this specific design was chosen, as opposed to some other design. That reason is given with practical grounding, so that the GM can understand what effects it had.