The smartphone ship has sailed long time ago, and no matter what magical flagship Microsoft releases, they would never gain dominance or even notability in the mobile space. Nadella himself as admitted as much. They're probably not going to focus on winning that lost battle, just as they're not going to try to beat Google with Bing.
With all the great execution of Windows and Office, Steve Ballmer bled a lot of money on other businesses, constantly trying to overtake incumbent with generally inferior products that offered too little differentiation. Don't forget the Zune, the Kin and the early Windows phones, Bing, Microsoft Stores and so on.
Almost no new line of products released by Microsoft during the Ballmer years actually managed to gain market - the Xbox being the sole exception, since it actually managed to differentiate itself well.
At the same time, Microsoft was very slowly, but also very surely, bleeding market share at markets they traditionally dominate like desktop browsers and consumer OS.
I think Tim Cook at the very least didn't get any embarrassing failure on his name yet, and iOS is not stagnating the way Internet Explorer, Office and Windows Mobile did.
