I may be wrong. To confirm whether things changed or not, we'd need to get Google insiders to speak out on that subject.
There is another possibility, that direct (verbal) user feedback is discounted as being "anecdotal" and not included when making "data driven" design decisions. But as you mentioned, this is all speculation without an insider's POV.
My intuition, however, is that their data-driven technique over-optimizes the various minutiae while allowing broader flaws to persist. I'd chalk that up to a lack of design vision to guide the testing.
I think there was a clear line drawn at least with the G+ integration, since they started consolidating the appearance of all services under the same UI and same color codes. There is a now a clear "design vision" in Google (even if it clearly sucks bad) and it's clearly not as Engineers-driven/Fonctionality-driven as before. Having Icons without text next to it is not just a style issue: it's a well known flaw in terms of usability. Everyone knows icons+text are superior to icons only. Especially when your icons are dark grey on light grey background. No differentiation whatsoever. I can't believe someone was actually paid to do this.
The page has since changed again, I believe, and it's even more of a mess. Scanning the page while scrolling is nearly impossible unless you've very carefully placed your mouse pointer over elements that do not expand on hover. (It's really maddening and I barely use the page anymore because of it.)