This is a reasonable take in my view. When you acquire a company, you don't get to replace their entire tech stack on day 1.
And sometimes there are chains of dependencies that need to be swapped out in sequence.
So from acquisitions alone it would seem reasonable to expect that Microsoft at any point in time has at least a handful of usages of certain SaaS offerings, even if MS themselves offer their own versions of those services.
That said, the surface area of these "unofficial" 3rd party systems is likely to be quite small in comparison to whatever their official tech stack looks like (which does -- I would assume -- centre around Azure AD). I'm not expressing an opinion on whether the GP is correct to make this link...
I've worked with some very large companies where internally they (surprisingly to me) make use of competitors' products even when that company makes their own version of that product. There are all sorts of legitimate reasons why this happens.
And sometimes there are chains of dependencies that need to be swapped out in sequence.
So from acquisitions alone it would seem reasonable to expect that Microsoft at any point in time has at least a handful of usages of certain SaaS offerings, even if MS themselves offer their own versions of those services.
That said, the surface area of these "unofficial" 3rd party systems is likely to be quite small in comparison to whatever their official tech stack looks like (which does -- I would assume -- centre around Azure AD). I'm not expressing an opinion on whether the GP is correct to make this link...
I've worked with some very large companies where internally they (surprisingly to me) make use of competitors' products even when that company makes their own version of that product. There are all sorts of legitimate reasons why this happens.