I agree, that it all seems to point in the direction of Telekom. But it isn’t that easy. Switching DNS didn’t work for me at all. I have no problems with MSFS 2020 or any other application, nor do I have any packet losses. Telekom definitely doesn’t “throttle” anything. And at times it does work for me. Just not at times with typical high demand from flight simmers.
For me that points in the direction of insufficient infrastructure on Microsofts side. Or they are doing something completely different then all other applications, which happens to not being handled good by Telekom infrastructure. In that case, Microsoft should avoid such specialties - or reach out to Telekom to explain, what they are doing differently.
That’s my 5 cents and possibly also besides the truth… 