This is not entirely true. Yes, Ballmer made many mistakes, but he also architected one of the most sustainably profitable enterprise software businesses (on the heels of all MS software products we love to hate). These enterprise customers are more than knees deep with Microsoft, and deep account penetration bought at least 5 years for Satya to steer the ship in the right direction (giving up on B2C mobile, Windows obsession, etc.)

One of the most common biases I see in how we assess leaders is how we try to attribute success & failure to a single person at a discrete point in time (ex: Here in the US, the extreme Left claims Trump is taking credit for Obama's foundational effort for the economy while the extreme Right says it's all Trump). In reality, it is never that simple nor discrete but rather complex and continuous.