I wish for once people on Hacker News didn't make sweeping statements about a profession that isn't theirs? Most good designers will recognize those are bad design choices.
> "Why do programmers go out of their way to put bugs in software?"
We have no problem mocking programmers when AWS goes down, log4j or FB messes up. I expect designers from a company as big as Amazon to not fumble about the fundamentals of what makes legible text.
I've done it before and many agree (72 upvotes): https://news.ycombinator.com/item?id=24965346
b) It looks pretty close to black to me.
In typography, book weight for print fonts is usually lighter (congruent to W3 standards). This is because of the slight blotting effect when printed on paper. But for screen use, it is actually slightly bolder (450-ish). Here is an example from Lineto foundry: https://lineto.com/typefaces/moderne
Book weight is between Regular and Medium.