I have no doubt Nadella is a better CEO than Balmer, he's definitely been a better resource allocator. But MSFT's EPS has. basically been flat since before Satya arrived. It's stock price tripled because it's a bull market, no other answer necessary.
Microsoft seems grossly overvalued with a P/E of 50. For the longest time, Microsoft had the same P/E as the s&p500 (10-18), but now it’s 56% above the s&p500’s (23). If Azure were to fall behind, I could see msft’s stock dropping by 40% and kept aloft mostly by it’s dividend, Money has been pouring into the whole tech stock sector after that cryptocurrency selloff earlier this year.