You are also assuming that A) Microsoft cannot learn from past mistakes, and B) the blame for Skype falls squarely on Microsoft's shoulders.

Discord is currently at the top of its game (more like PowerPoint was), whereas Skype was suffering from mismanagement under eBay. Microsoft was supposedly hands off on Skype in the first few years post-acquisition and most of the mistakes that killed Skype were some combination of projects already started under eBay management or still all planned "inside the house" at Skype. (Microsoft in 1987 was said to be hands off with PowerPoint for the first few years following acquisition so as not to interfere with the creative efforts already in progress. Microsoft in 2021 is supposedly still remaining pretty hands off in GitHub management, other than replacing the outgoing CEO.) Microsoft's MO seems to be to give acquisitions enough rope to either succeed or hang themselves, and Skype sounds like they took that second option.

No, I'm reserving judgement. I hope Microsoft won't ruin Discord, not least because I use it fairly heavily and I don't want to have to switch (again).

I'm just noting that at least from the outside, the Skype case looks much more relevant to this situation than the PowerPoint one.