He was already killing it when he was at Microsoft. (I can tell, because I worked at a pretty big EU based Microsoft partner at the time).

Note that pretty major stuff like .NET (developers, developers, developers!), Windows Mobile, Windows Phone, Surface, Xbox, and Azure all got launched under his watch.

Sometimes I even think Nadella fucked it all up. Windows 10 was meh, Windows 11 is shit, Mobile was killed even though the Nokia phones were top notch, Sony just publishes first party games on PC to earn extra cash while MS needs to do it to keep the Xbox division alive (because everything released on day 1 on Xbox is also released on PC so why bother with a console...), the AI hype will not lead anywhere, and I could go on and on...

... but oh well.