My opinion is that the failure of Microsoft has less to do with Ballmer than with the absence of a Steve Jobs.
My experience with large corporations is that they naturally produce mediocrity. The ownership of the final product or service is too diluted, with too many people involved, pulling in too many conflicting directions. They employ people who individually know what "good" means and what should be done in an ideal world. But that knowledge and common sense gets lost with the bureaucracy and the scale of the organisation.
So unless you get someone at the top who will force the company to still achieve something great for their customers, you will end up with an MBA style manager who will make decisions based on options provided by his teams and get products designed based on specs from the top rather than trying to make something great.
A great example is Windows 8. I heard Sinofsky had already been sacked by the time he walked on stage to introduce Windows 8. Microsoft knew it was a shit OS, and decided to push it nevertheless. I have seen this happening so many times in other contexts.
But tablets are another example. Microsoft knew that tablets would be a big thing well before the introduction of the ipad. In fact I remember a pre-ipad interview of Ballmer where he was deploring that the Windows tablets never took off. The problem was that windows-based tablets were too mediocre to create a market.
But Apple is moving in that direction too now. The user experience is deteriorating with every iteration of iOS. I can't think that someone at Apple thinks it's a good user experience to nag their users with all of their services (Apply Pay, iCloud, Apple Music, etc) over and over, with multiple buttons to click to opt out. That will ultimately bite them too. Not overnight, but over 10 years like with Microsoft. Not Tim Cook's fault. That's what large corporations do.