It's just teams replacing skype and easy enough to disable, the issue with IE was strong arming I doubt Microsoft is going to strong arm slack at any other level.. same goes for Onedrive/iCloud
Relevant snippet from the Wiki article on the Microsoft antitrust lawsuit:
"The plaintiffs alleged that Microsoft had abused monopoly power on Intel-based personal computers in its handling of operating system and web browser integration. The issue central to the case was whether Microsoft was allowed to bundle its flagship Internet Explorer (IE) web browser software with its Windows operating system. Bundling them is alleged to have been responsible for Microsoft's victory in the browser wars as every Windows user had a copy of IE. It was further alleged that this restricted the market for competing web browsers (such as Netscape Navigator or Opera), since it typically took a while to download or purchase such software at a store. Underlying these disputes were questions over whether Microsoft had manipulated its application programming interfaces to favor IE over third-party web browsers, Microsoft's conduct in forming restrictive licensing agreements with original equipment manufacturers (OEMs), and Microsoft's intent in its course of conduct."
To draw parallels between that lawsuit and this discussion:
1. I guess the download effort of Slack isn't really a concern anymore. And while I have no idea of the feature parity between the free versions of Teams and Slack, the free versions of both apps should probably be sufficient for casual users (i.e. the inertia of entering payment information is not a concern).
2. I have no idea if Microsoft has added any secret sauce to Windows 11 that would make Teams run better on Windows owing to tighter in-house integration. But if this is true, and Slack (or other competitors) won't be able to use this to boost their own performances as much, I suspect this could be a big deal.