They currently have around 20% market share (as Internet servers - much higher inside business LANs), which is a very nice chunk. And I'm sure encourages them to keep working on it.
Frankly the tooling for MS server keeps it in the hunt - they really understand the concept of making things easier to use.
Extremely big doubts about this. How would anyone even know? All the hyperscale datacenters built by FAANG must be 99.9% Linux, and those DCs alone would probably be enough to make 20% impossible to hit for windows.
(Scroll down to servers)
Incidentally this is public facing Internet servers. The % -inside- enterprises us much much higher.
Tools like Active Directory allow you to scale enterprise operations, which is important for companies that have hundreds-of-thousands of desktops etc.
In any event your estimate of 99.9% is unlikely. AWS offers Windows based EC2 instances, and one presumes they're not doing that for 0.01% of the market. Azure will likely have an even higher %.
From the data though, not just guessing, I'd say it's about 20% overall.
I can believe private enterprise usage is higher, but I imagine FAANG and similar companies also have quite a lot non public Linux servers. Not trying to rebut your overall point, but I'm not sure the total non public % is much different.
We know that all the top 25 websites are 100% Linux and represent a lot of servers each.
Also a whole lot of that cited report seems to be misidentified. The top Windows site other than Microsoft properties listed is nih.gov, which looks like Drupal on Linux behind Akamai GHost -- all Linux.
I do accept that Windows is probably about 20-25% of server instances and slowly contracting. But public facing webservers and the infrastructure that directly supports them? Nothing close to this.