Well put. Google is a data-driven company with the ability to test designs over millions of users (although Jakob Nielsen's work has shown that you reach the point of quickly diminishing returns after testing with 5-10 users).
I've spent quite a bit of time implementing Material Design for http://recent.io/, and then testing the design with normal, not especially tech-savvy users. My impression is that Material Design is a way to simplify and standardize app UIs (to increase app usage overall), and import visual cues from the paper world. It's very thoughtful approach, probably better than iOS, and I say this as someone whose primary mobile device is a new iPhone and who has owned an iPhone since the day it went on sale.
But what works for most people may not work for HN power users. Hence the complaints on this thread.