Is see what you mean. But switching the DNS servers doesn’t mean switching the ISP. It’s just changing the way you access the data via the same ISP.
So my thinkgin is: if the rest of the world has little or no problems with the bandwidth, problems in one specific country with one specific ISP are reported disproportionately and switching the DNS servers (or using a VPN in a different country) solves the problem. That’s extremely suspicious.
I’m certainly no expert on data connections. But may there’s something that Telekom does differently when accessing data. After all: downloading one large file is different than streaming scenery data that may contain hundreds or thousands of files. So if for example Telekom throttles the number of files you can download and access simultaneously that would also kill your bandwidth quite effectively. Also there certainly are different ways to manipulate how data is transmitted or there’s the possibility that the Telekom DNS servers don’t work as well as others. No idea really. Just throwing out some ideas.
In addition I also solved my streaming problems with Disney+ by switching to Cloudflare DNS in my router. So this makes two streaming problems from two completely unrelated sources that improved radically by removing the Telekom DNS servers from the equation. To me this makes it more and more unlikely that the problem lies with Microsoft and points to Telekom. And of course I’m not the only one with a similar story.
Without knowing more about how the internet actually works I can’t be sure, but from my limited understanding I’d bet money on Telekom being the culprit here.