They've long been quite mediocre judging by the incredible long hours of those working there and shit quality of basically any technical framework they put out.
They have shoved tons of resources into some things (such as Android) and thus at times succeeded (though usually they don't), but in terms of quality from a technical point of view (i.e. software design, technical architecture) their stuff looks like it was hammered together by a bunch of junior devs.
Lucky timing followed by some smart strategical decisions (and, seemingly, lots of money together with a throw everything at the wall and see what sticks management strategy) are what made Google, not excellence.