Or perhaps Google "got" design before, but didn't realize it.
Speed, functional value (as you said), simplicity, and such really ought to be considered part of design just as much as a visually appealing set of colors on an interface is.
To be fair, I think that the transition is still ongoing.
On Android side, the support lib fell really short last year with Lollipop. You could implement a lot of material goodness, but had to do 90% of the work yourself.
Something like a collapsing ActionBar is clearly doable but needs some time that won't be devoted to polishing other parts of the app.
Another consequence is that since there was no common implementation, there were small design differences on many elements among Google apps.
With the new support lib (22.2), Google has released a design lib which implements some material elements.
With this common base, I hope to see the design of the different first party apps harmonize a little bit more in the coming months.
Whether or not Design at Google is a move of some import is yet to be tested. Google is a heterogenous company with many different assets. It will take time for assets to upgrade, quirks ironed, old UX habits forgotten. Certainly "feels" that unifying/upgrading design is a good move.
Also, while I absolutely hate even firing up Maps (but I need to), I find that people, whose first experience with them is the new interface, like it very much.
The original article doesn't really prove anything. Someone used to think Google's design was bad, and now thinks it's nice.
Google did well before they got design, but they have probably widened their audience and increased conversion by getting design so increasing their profitability.
Aesthetically pleasing design is neither necessary nor sufficient to be a successful, but it definitely helps.
"Do I dare to say this somehow shows the relative unimportance of design?"
When design is about cramming some animation in just about everything you can show on the screen, and about how fancy your colors are going to be – yes, I agree, it's relatively unimportant.
But real design is not about that at all. In fact, functionality has been part of the core debate in design, for at least a century now. Ask any designer – not only the ones dealing with UI, and they'll tell you.
Google is/was quite successful before they got design (let's say success in this context means something like: a large audience).
And even when they decided to get design: it took them a relatively short amount of time to get things "right".
I agree Material Design looks very nice. But I think functional value (just picking a term here) is so much more important, by an order of magnitude.