I don’t think you’re quite grasping the situation here. Slack does not come preinstalled on any system, Teams does. That is the whole point, unfair competition. Large companies have a history of bullying smaller ones. Any action against these giants is long overdue and very necessary.
Slack did not file a complaint because they’re losing. This is what it says in the article:
Slack filed a complaint with the EU in 2020, claiming that Microsoft was “force installing [Teams] for millions, blocking its removal, and hiding the true cost to enterprise customers.”
And this is investigated 3 years later than the complaint. Microsoft has a history of installing bloatware and changing default clients to open with their own software.
Lynx?