You're gonna infuriate lots of CSS people! That's the basis of modularity: you can just move around a component anywhere on the page, it will keep its styling (thanks to classes like header--large) and not be disturbed by its surroundings.

Personally, I agree with you, and think it's a bad approach. Elements should be able to be styled according to context.

Let's say I have 2 columns: "main" and "sidebar". I have a list of my latest articles in "main". I want to show another list of articles in my "sidebar", but display them smaller, because it's secondary content.

Why should I have to add the ".post--small" class to all my posts? Why can't I use the context of the parent ".sidebar" and use that in my CSS? I could then keep the exact markup for all posts across the website.

"Ideal situation, parent container media queries"

Yes, that's exactly what CSS is missing, but you found the reason why it hasn't been implemented: circular dependency issues.