Not sure exactly what evidence I can show you other then myself being a sysadmin for companies who used the M365 suite and refused to use anything other then teams for communication. Anytime we brought up an alternative (even Zoom) it was always shot down by finance who said “we already have Teams”. Same thing for Slack.
https://techcrunch.com/2020/07/22/slack-has-filed-an-antitrust-complaint-against-microsoft-teams-in-the-eu/
Not sure exactly what evidence I can show you other then myself being a sysadmin for companies who used the M365 suite and refused to use anything other then teams for communication. Anytime we brought up an alternative (even Zoom) it was always shot down by finance who said “we already have Teams”. Same thing for Slack.