It's unfair to discount Google's early days. They DID have technical excellence. Search was leagues better than the competition. Gmail was an amazing leap from other providers. Android started as trash but improved rapidly. The Nexus line of phones was amazing. Google Maps was a huge improvement over what else existed. They did a lot right.
I can't pinpoint exactly when the fall started. Was it when Pichai became CEO? When they removed "don't be evil?" I remember a speech Pichai gave where he talked about "more wood behind fewer arrows" as why they were getting rid of employee child projects, so maybe it was that.