I see no evidence for your statement.
Ballmer 4x-ed MSFT revenue during his tenure.
He made far more money for MSFT than Gates ever did, and his growth track record is better than Satya so far.
Ballmer pushed XBox, Azure, Office/Cloud, re-orged the sales teams. Increased revenues for all the other major product lines.
Bing and Mobile were a fail, but they did other things well, moreover, they're up against the top 2 companies in the world in Search and Mobile - no easy feat.
All of your points are descriptive, but they don't really represent huge materiality in terms of business outcomes.
MS was never losing developers.
It's 'OSS contributions' really don't make that much of a difference.
Revenue under Satya has been up and down, with no real progress for his first several years until 2018 (2015 being the watermark).
MSFT today was made by Ballmer, most of the things you indicated are good, but not hugely fundamental.
You seem to equate revenue with success, which is not how this stuff works. Shareholder value is actually tied to the prospects for long term success (accumulated profits over time). MS shares were considered overvalued, not undervalued when Ballmer left (or depending on your interpretation, fired by an unhappy board).
Its OSS contributions are critical to both MS and how well it is able to convince developers to build on top of MS platforms. It's critical for it's credibility with Azure. I know people that now consider this a serious alternative to AWS or Google cloud that for sure don't have any interest on running C# on Windows Server while using SQL server. But it sure is a nice way to run some Linux stuff these days.
Satya Nadella also had to absorb a lot of the Ballmer era mistakes. Like paying five billion for the right to shut down an organization (Nokia's Phone business) for probably billions more. As I recall, that was one quarter where MS indeed made a historically unique loss and Ballmer pushed that deal through. Bing indeed is another dud. Windows Phone itself of course was the latest in a series of failures for MS to capture the mobile market that date back to last century.
The fact that it took a few years to recover after Ballmer left strongly suggests that 1) there were indeed problems in MS (i.e. shareholders were right) 2) Nadella addressed those problems. MS is of course valued around a 1 Trillion or so now. This may have a thing or two to do with the fact that he's not doing that bad of a job and that their future looks a lot brighter than a few years ago.
I grew up in the nineties; things were different then. Visual Studio was the go to product for many developers and developing on windows was a given. Macs didn't become useful as developer machines until a decade later and Linux was a something you ran in your closet or on a old hand me down PC (been there done that). That changed under Ballmer's rule and he failed to adapt. He alienated developers and failed to move windows forward; all while bashing Linux and the Open source community in futile attempts to stem the bleeding of mindshare, revenue, and share holder value.
Fast forward five years or so since Nadella took over and the stock has responded positively to post Ballmer changes by Nadella to bring MS into this century after what was a lost decade.
MS now does open source and established itself as a credible player in the OSS community, it killed off windows phone, opened up the lucrative office ecosystem to non windows platforms by e.g. treating Android and IOS as first class citizens and supporting things like Chrome OS. By embracing linux and open source, and by turning Azure into a very competitive product that mostly runs Linux. He just took Edge out the back and shot it as well.
The net result of all this is that he re-established MS as a company that appeals to developers because despite his famous Mantra, developers were running away under Ballmer. VS Code, having SQL Server supported on linux, supporting Linux and contributing to it, embracing the wider C# ecosystem outside of the Windows silo, buying Github, etc. are all clever moves that rebuilt lost trust. All these things were unthinkable under Ballmer. Even Windows 10 is starting to look pretty nice to people like me with it's linux subsystem, Docker support, and nice hardware options.
As a consequence they have a lot of healthy growth in their cloud business because developers take them serious again. Shareholders are liking this and their prospects for more growth through a portfolio that is no longer just wintel laptop based revenue.