I'm glad I'm not the only one thinking that. These are such minutiae. Where's the discussion about humans? They're probably the most important part of your system, and the most chaotic, and the part that needs the most careful design.

It's hinted at a little bit in the OP, with:

> What does good system design look like? I’ve written before that it looks underwhelming

This is because there are humans in your system! Other developers! You in the future! You have to resort to heuristics like "simple == good" because you're only looking at a small part of the whole system.

And zoom out even more, you get to the actual users. How do they interact with the system? If you implement a rate limiter, how do the users respond when they hit it? Do they just spam-refresh the page? Open more tabs? Use their phone? Do they develop weird superstitions about it? Do they spam-call your phone support lines? Does your response to a thundering herd anticipate the second-order impact of your phone support lines being DDOSed?

Exactly. Systems design at the SE level is socio-technical: the humans and their feedback loops matter as much as the tech. Many “good” designs fall apart because they forgot that the system boundary doesn’t stop at the codebase.