It's funny, the more time goes by the more I miss iOS 6 and company. Comparing flat UI design to Swiss design from the 50s is missing the obvious difference that minimal Swiss design was about presenting information, not creating an interactive interface.
As the linked article points out, discarding affordances has a very real cost to someone learning the interface - it becomes harder to separate interactive elements from non interactive ones and harder to tell "on" from "off" (I STILL can't tell if iOS's shift is on by looking at it [1]). The desire to present information in a modern/minimalist way is at odds with this.
My personal opinion is that what you call "wider design context" is pure fashion. Yes, flat is fashionable, but it's just not as good at the job of communicating the nature of UI elements to the user.
[1] Edit: Just to add, Apple's difficulty with making the state of the shift key obvious is a microcosm of this overall problem. The expressive power of flat design language is so limited that indicating the state of a single element is problematic despite several attempts. iOS 9 finally solves this by changing the case of every letter on the keyboard to make it obvious.